a. Jim is at the door. ______ wants to see you.
b. Someone is at the door. ______ must be Jim.
A. That, It B. It, He C. He, It D. Who, He
此题应选C。第a. 句填代词 he，是因为前面一句用了Jim这一身份和性别都很明确的名词；第b. 句填代词it，是因为前面一句了someone这一指代不明确的代词。
一般说来, 在指代身份或性别明确的人时, 通常要根据情况用代词he/she；若是指代身份或性别不明的人, 则用代词it：
I don’t know who it is. 我不知道那是谁。
A tall man stood up and shook hands with her. It was the general manager. 一个高个子站起来同她握了手，他是总经理。
Someone must have been here. But we have no idea who it was. 一定有人来过，但我们不知道是谁。
There was somebody standing in front of the shop, but I couldn’t see who it was. 商店前站着一个人，但我没看清是谁。
A: Who has let out the secret? 是谁泄漏了密秘?
B: It must be a big mouth. 一定是个快嘴。
A: I hear a knock at the door. 我听见有人在敲门。
B: It must be the postman. 一定是邮递员来了。
A: Do you know who that is? 你知道那个人是谁吗?
B: I suppose it is Mary’s father. 我想那是玛丽的父亲。
