The kind-hearted couple decided to adopt the boy parents had been killed in an accident.A

问题补充：

The kind-hearted couple decided to adopt the boy parents had been killed in an accident.

A. of whom

B. with whom

C. on whom

D. in whose

答案：

(答案→)A. of whom

B. with whom

C. on whom

D. in whose

解析：考查介词与关系词引导的定语从句。先行词the boy与parents之间是从属关系，因此选择A项。