Since May 12th, relief (救援) soldiers _____ thousands of people's lives in the earthquake (地震) area in

Sichuan.[ ]

A. have saved

B. have seen

C. have found

二尖瓣狭窄时，切面超声心动图可见（）

A.二尖瓣口面积大于2.0cm

B.左心室扩大

C.瓣尖部活动幅度增加

D.二尖瓣前后叶增厚