1.With China ________ in the world trade more frequently, the world economy is developing more rapidly and steadily.           

A. participating              B. to participate              C. participated              D. being participated

2..When asked about his childhood, the man was found       . Obviously, it is a scar he doesn't want to be touched.           

A. choked up                        B. sprung up                        C. split up                        D. broken up

3.Exactly ______ the potato was introduced into Europe is uncertain, but it was probably around 1565.

A. whether                                  B. why                                  C. how                                  D. when

4..If you have a job£¬______ yourself to it and finally you'll succeed.
A. do devote                     B. don't devote                     C. devoting                     D. not devoting

5.—I don't think I can go any further.

— ______. You can do it if you keep trying!

A. Come on                   B. Take it easy                   C. Never mind                   D. It doesn't matter