常用于混悬剂与乳剂等分散系的粉碎的机械为

A．球磨机

B．胶体磨

C．气流粉碎机

D．冲击柱式粉碎机

E．锤击式粉碎机

It was after careful consideration ________we decided to take action.

A．which

B．that

C．why

D．when