对于STM-1信息,每帧有()个字节用于段开销。
A.27
B.45
C.72
D.81
参考答案:C
离心泵加填料时正确的方法是()。
A.填料要长短合适,接缝严密
B.几根填料的头要互相错开
C.压盖松紧要合适
D.填料每一圈的头可以互相搭接
Our English teacher is ill, and we are all ______ her health.
A.concerned about
B.careful of
C.grateful for
D.calm down