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