Those were the graduate assistants ______ to do the research work in the lab.

A．to whom it was their responsibility

B．whose responsibility there was

C．whose responsibility was

D．of whom with the responsibility

由予搅拌操作的多种多样，也使搅拌器存在着许多形式，典型的搅拌器形式有（）、推进式、锚式、螺杆式等。

A.分离式

B.桨式

C.涡轮式

D.框式