---What are you busy with ?--- We are carrying out a research the causes of cancer.A. in

问题补充：

---What are you busy with ?

--- We are carrying out a research the causes of cancer.

A. into

B. onto

C. to

D. in

答案：

(答案→)A. into

B. onto

C. to

D. in

解析：考查介词：do/carry out research into/on对…做研究，句意：--你在忙什么？--我们在做一个关于癌症原因的研究。选A。