______ we think of Ben, we have to admit that he is a highly competent man.

A．However

B．Whether

C．Whichever

D．Whatever

第一心音的产生，错误的是

A．以上均不是

B．半月瓣开放的振动

C．二尖瓣关闭时瓣膜的振动

D．发生在心室开始收缩时

E．三尖瓣关闭时瓣膜的振动