He has a good knowledge of electricity, ________ helps him a lot in his work．

1. A.
   that
2. B.
   who
3. C.
   when
4. D.
   which

 He has a good knowledge of electricity, ______helps him a lot in his work.

A. that     B. who     C. when     D. which

He has a good knowledge of electricity, ______helps him a lot in his work.

A. that　　　　　　 　　　　　　　　　　　　　　　　　　  B. who　　　　　　

C. when　　　　　　 　　　　　　　　　　　　　　　　　　　　  D. which

A. that　　　　　　 　　　　　　　　　　　　　　　　　　  B. who　　　　　　

C. when　　　　　　 　　　　　　　　　　　　　　　　　　　　  D. which