–Do you know the boy is standing under the tree?-- Yes he is my friend Peter.A. whatB.

问题补充：

–Do you know the boy is standing under the tree?

-- Yes, he is my friend, Peter.

A. what

B. who

C. whom

D. whose

答案：

A. what

(答案→)B. who

C. whom

D. whose

解析：定语从句的考察 先行词the boy是“人”，在定语从句中作主语，故用关系代词who.