名词性从句选择题 就是做什么成分的那个

名词性从句选择题 就是做什么成分的那个
1.___do you think is right___difficulties you may have?答案是A为什么不选D呢?
A.What,whatever B.That ,that C.Which ,what D.How,whatever
2.___will go makes no difference.答案是B为什么不选D呢?
A.Whether B.Who C.What D.How
3.It was about 600 years ago___the first clock with a face and an hour hand was made.答案是B为什么不选C呢?
A.until B.that C.before D.when
4.I don't know___we are going to have this meeting.Which answer is wrong?答案是B为什么不选D呢?
A.why B.what C.where D.whether