She brought with her three friends, none of           I had ever met before.

A．them

B．who

C．whom

D．these

整立杆塔时，要做到“四点一线”，如下表达正确的是（）。

A.总牵引地锚

B.制动系统中心

C.抱杆顶点

D.电杆根部