if you want to do something or you won’t be able to do it well.A. To try your bestB. Try

问题补充：

if you want to do something, or you won’t be able to do it well.

A. To try your best

B. Trying you best

C. Try your best

D. Unless you try your best

答案：

A. To try your best

B. Trying you best

(答案→)C. Try your best

D. Unless you try your best

解析：考查非谓语动词和祈使句。句意“尽最大努力，如果你想做一件事的话，否则你不会做好它。”A表示目的，B表示伴随；D中的unless不能与if连用。C项是祈使句，符合题意。故选C。