使匈奴再也无力与西汉对抗的事件是[ ]
A、夺回河套和河西走廊地区
B、经过漠北战役的沉重打击
C、匈奴分裂为几部,彼此攻杀不休
D、呼韩邪单于向汉称臣
答案:B
I never there before. [ ]
A. have; been
B. have; gone
C. have; been to
D. have; gone to
心脏瓣膜病变中,最多见的是
A.二尖瓣病变B.三尖瓣病变C.主动脉瓣病变D.肺动脉瓣病变E.联合瓣膜病变