风湿性心瓣膜疾病最常见侵犯的瓣膜是（）
A.主动脉瓣
B.肺动脉瓣
C.二尖瓣
D.三尖瓣
E.人工瓣膜
参考答案：C
It is not always easy for the general public to see _____use a new invention can be of to their daily life.
A．which
B．what
C．that
D．whose
下面各数中，只读一个零的是[ ]
A．902600
B．93000390
C．5080203
