一道专四英语选择题,急

一道专四英语选择题,急
Which of the following italicized parts is used as an object?
A.What do you think has happened to her?
B.Who do you think the visiting professor is?
C.How much do you think he earns every month?
D.How quickly would you say he would come?
WHAT ,WHO ,HOW MUCH,HOW QUICKLY,分别在句子做什么成分,为什么