某同学在进行研究性学习中，引用了下组数据。结合所学知识，判断他可能研究的主题是 <table style="BORDER-BOTTOM: medium none; BORDER-LEFT: medium none; BORDER-COLLAPSE: collapse; BORDER-TOP: medium none; BORDER-RIGHT: medium none; mso-table-layout-alt: fixed; mso-border-alt: solid windowtext .25pt; mso-padding-alt: 0cm 0cm 0cm 0cm; mso-border-insideh: .25pt solid windowtext; mso-border-insidev: .25pt solid windowtext" border="1" cellspacing="0" cellpadding="0" _dj="MsoNormalTable"><tbody><tr style="HEIGHT: 9.85pt; mso-yfti-irow: 0; mso-yfti-firstrow: yes"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext 1pt solid; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 118.95pt; PADDING-RIGHT: 5.4pt; HEIGHT: 9.85pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt" width="159">年代</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 61.35pt; PADDING-RIGHT: 5.4pt; HEIGHT: 9.85pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt" width="82">道、路、省</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 34.3pt; PADDING-RIGHT: 5.4pt; HEIGHT: 9.85pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt" width="46">州数</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 44.9pt; PADDING-RIGHT: 5.4pt; HEIGHT: 9.85pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt" width="60">郡国数</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 104.35pt; PADDING-RIGHT: 5.4pt; HEIGHT: 9.85pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt" width="139">县、邑、道、侯国等</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 56.1pt; PADDING-RIGHT: 5.4pt; HEIGHT: 9.85pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt" width="75">户数（万）</td></tr><tr style="HEIGHT: 13.85pt; mso-yfti-irow: 1"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext 1pt solid; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 118.95pt; PADDING-RIGHT: 5.4pt; HEIGHT: 13.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="159">西汉平帝（1—5）</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 61.35pt; PADDING-RIGHT: 5.4pt; HEIGHT: 13.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="82">—</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 34.3pt; PADDING-RIGHT: 5.4pt; HEIGHT: 13.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="46">13</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 44.9pt; PADDING-RIGHT: 5.4pt; HEIGHT: 13.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="60">103</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 104.35pt; PADDING-RIGHT: 5.4pt; HEIGHT: 13.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="139">1587</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 56.1pt; PADDING-RIGHT: 5.4pt; HEIGHT: 13.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="75">1223</td></tr><tr style="HEIGHT: 14.85pt; mso-yfti-irow: 2"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext 1pt solid; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 118.95pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="159">唐贞观十三年（639）</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 61.35pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="82">10道</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 34.3pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="46">358</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 44.9pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="60">—</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 104.35pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="139">1551</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 56.1pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="75">缺</td></tr><tr style="HEIGHT: 14.85pt; mso-yfti-irow: 3"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext 1pt solid; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 118.95pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="159">唐开元二十八年（740）</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 61.35pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="82">15道</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 34.3pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="46">—</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 44.9pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="60">328</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 104.35pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="139">1573</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 56.1pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.85pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="75">841．3</td></tr><tr style="HEIGHT: 21.25pt; mso-yfti-irow: 4"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext 1pt solid; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 118.95pt; PADDING-RIGHT: 5.4pt; HEIGHT: 21.25pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="159">宋开宝（968—975）末</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 61.35pt; PADDING-RIGHT: 5.4pt; HEIGHT: 21.25pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="82">—</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 34.3pt; PADDING-RIGHT: 5.4pt; HEIGHT: 21.25pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="46">297</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 44.9pt; PADDING-RIGHT: 5.4pt; HEIGHT: 21.25pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="60">—</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 104.35pt; PADDING-RIGHT: 5.4pt; HEIGHT: 21.25pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="139">1086</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 56.1pt; PADDING-RIGHT: 5.4pt; HEIGHT: 21.25pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="75">309</td></tr><tr style="HEIGHT: 14.1pt; mso-yfti-irow: 5; mso-yfti-lastrow: yes"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext 1pt solid; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 118.95pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.1pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="159">宋宣和四年（1122）</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 61.35pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.1pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="82">26路</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 34.3pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.1pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="46">288</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 44.9pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.1pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="60">—</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 104.35pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.1pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="139">1234</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; WIDTH: 56.1pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.1pt; BORDER-TOP: medium none; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .25pt; mso-border-left-alt: solid windowtext .25pt; mso-border-top-alt: solid windowtext .25pt" width="75">—</td></tr></tbody></table>