The first thing we should do is to tell him the news.AwhoB. whichC. thatD. whom

问题补充：

The first thing we should do is to tell him the news.

Awho

B. which

C. that

D. whom

答案：

A. who

B. which

(答案→)C. that

D. whom

解析：句意：我们应该做的第一件事情就是要告诉他这个消息。定语从句的先行词受到序数词的修饰时，关系代词只能用that来引导；故选C。