定语从句（1）
1. We should learn from those ______ are always ready to help others.
  A. who          B. whom      C. they       D. that
2. Mr. Herpin is one of the foreign experts who ______ in China.
  A. works         B. is working   C. are working   D. has been working
3 . Tom is the only one of the students who ______ to Shanghai.
  A. have gone       B. have been    C. has been     D. had gone
4. I, ______ your good friend, will try my best to help you out.
  A. who is        B. who am     C. th ...