下表反映了英国农业人口的变化，导致这一变化的主要原因是<table style="MARGIN: auto auto auto 0.75pt; BORDER-COLLAPSE: collapse; mso-table-layout-alt: fixed; mso-padding-alt: 0cm 0cm 0cm 0cm" border="0" cellspacing="0" cellpadding="0" _dj="MsoNormalTable"><tbody><tr style="HEIGHT: 16.4pt; mso-yfti-irow: 0; mso-yfti-firstrow: yes; mso-height-rule: exactly"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext 1.5pt solid; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 0cm; WIDTH: 135pt; PADDING-RIGHT: 0cm; HEIGHT: 16.4pt; BORDER-TOP: windowtext 1.5pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-height-rule: exactly" valign="top" width="180">年份</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 0cm; WIDTH: 180pt; PADDING-RIGHT: 0cm; HEIGHT: 16.4pt; BORDER-TOP: windowtext 1.5pt solid; BORDER-RIGHT: windowtext 1.5pt solid; PADDING-TOP: 0cm; mso-height-rule: exactly; mso-border-left-alt: solid windowtext 1.0pt" valign="top" width="240">   1840    1870    1900    1920</td></tr><tr style="HEIGHT: 18.3pt; mso-yfti-irow: 1; mso-height-rule: exactly; mso-yfti-lastrow: yes"><td style="BORDER-BOTTOM: windowtext 1.5pt solid; BORDER-LEFT: windowtext 1.5pt solid; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 0cm; WIDTH: 135pt; PADDING-RIGHT: 0cm; HEIGHT: 18.3pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-height-rule: exactly; mso-border-top-alt: solid windowtext 1.0pt" valign="top" width="180">农业人口占总人口的百分比</td><td style="BORDER-BOTTOM: windowtext 1.5pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 0cm; WIDTH: 180pt; PADDING-RIGHT: 0cm; HEIGHT: 18.3pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1.5pt solid; PADDING-TOP: 0cm; mso-height-rule: exactly; mso-border-left-alt: solid windowtext 1.0pt; mso-border-top-alt: solid windowtext 1.0pt" valign="top" width="240">    22     14.8     8.4     7.1</td></tr></tbody></table>