题目内容：

谁能帮我解释解释这五道英语单选题?
1.--Did all these funny things happen in your club?
--No,it was in the class______I studied English.
A.when B.where C.that D.which
2.The bus rolled into the valley,____ over 20 deaths.
A.caused B.having caused C.causing D.to cause
3.I won't give in _____ great difficulties I come across in my life.
A.however B.whichever C.whatever D.wherever
4.It is such a difficult problem ___ no one can work out.
A.as B.that C.so D.thus
5.I'd rather you ____ there next week.
A.went B.go C.should go D.had gone
答案是BCCAA,我想让人帮我讲一讲为什么选这个答案.