装于屋架下面的板条吊顶，主要由（）组成。
A、平顶梁
B、平顶筋
C、吊筋
D、板条
参考答案：A, B, C, D
On the way to the supermarket , it suddenly _______ to me that I had forgotten to lock my car , so I hurried back to lock it .
A．happened
B．occurred
C．thought
D．came
二尖瓣狭窄时，首先引起心脏的（）.
A.左心室扩张
B.左心房扩张
C.右心室扩张
D.右心房扩张
E.以上都不是
