— Have you been here before?— Yes. This is the third time that I to Shanghai.A. comeB. ca

问题补充：

— Have you been here before?

— Yes. This is the third time that I to Shanghai.

A. come

B. came

C. have come

D. had come

答案：

A. come

B. came

(答案→)C. have come

D. had come

解析：考察固定句式中的时态。固定句式：It /That/This is the...time that sb have done sth；It /That/This was the...time that sb had done sth。“这是某人第几次做某事的时候了”；结合日常生活实际，能够计算到这是第几次做某事，表明该动作已经发生，因此，要用完成时态——主句用现在时，从句用现在完成时；主句用过去时，从句用过去完成时。本句前面使用了is。说明后面使用的是现在完成时。故C正确。