以下哪项是主动脉瓣关闭不全所致（）.
A.SAM现象
B.弓背样改变
C.钻石样改变
D.吊床样改变
E.二尖瓣前叶高频震颤
参考答案：E
Not knowing his address , she had some difficulty ________ his house.
A．finding
B．to find
C．found
D．find
体积相等的铜块和铝块，______块的质量大；质量相等的铜块和铝块，______块的体积大．
