声像图难以清楚显示脐索包膜和血管结构的原因是（     ）

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SQL Error: select id,body,options from ***_enewstiku where sourceid='25739' and id < 2163417 and id<>'2163417' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='25739' and id > 2163417 and id<>'2163417' order by id asc limit 5