I will be surprised if you can get Calvin who is very busy these tickets for you.A. buyB

问题补充：

I will be surprised if you can get Calvin, who is very busy, these tickets for you.

A. buy

B. buying

C. buys

D. to buy

答案：

A. buy

B. buying

C. buys

(答案→)D. to buy

解析：句意，如果你能让Calvin 为你买票，我会很吃惊，他是那样的忙。get sb. to do sth.意思是让某人做某事。