被检工件晶粒粗大，通常会引起：（）
A.草状回波增多
B.信噪比下降
C.底波次数减少
D.以上全部
参考答案：D
Look and write.（看图，写单词)
1. _______ 2. ______ 3. ______
4. ______ 5. ______
The result was not as good as expected but the ________ on his face told us that he was still very happy.
A．expression
B．impression
C．celebration
D．appearance
