定语从句的几个问题,急啊 忘解答!十分感谢

定语从句的几个问题,急啊 忘解答!十分感谢
he has got himself into a dangerous situation___he has no control.
A because B as C over that D over which选几 为什么
was it he who the professor regarded with such contempt?
这里用he who 而不是who he?为什么
sunday is a holiday,__most people do not go to work. 空中为什么是when而不是which?
from time to time we must look up words__空中用whose meanings we do not know 还是whose meanings we are not familar?为什么～希望有人告诉我 感激啊
1选d