问题补充：
— in this street? — I think Mr. Black is the richest man.
A. Whom do you think is the richest man
B. Who do you think is the richest man
C. Do you think who is the richest man
D. Do you think whom is the richest man
答案：
A. Whom do you think is the richest man
B. Who do you think is the richest man
C. Do you think who is the richest man
D. Do you think whom is the richest man
解析：题中do you think为插入语,疑问词在句中作主语。
