My head-teacher helped me a lot when I was in trouble. I do wish I could do something for

问题补充：

My head-teacher helped me a lot when I was in trouble. I do wish I could do something for him one day.

A. in turn

B. in common

C. in return

D. in theory

答案：

A. in turn

B. in common

(答案→)C. in return

D. in theory

解析：选项A“依次，轮流”； 选项B“共有”； 选项C“作为报答”； 选项D“在理论上”；句意：我的班主任在我困难时帮了我很多，我多么希望我有一天能够为他做件事作为报答。