1.When I try to find out ______that prevents so many people from taking part in the program,it seems to me that there are two main causes.
A.what it is B.what it does C.why it does D.why it is
2.I'd appreciate_______you could give me some advice.
A.it B.that C.it if D.when
3.I hate it ________people speak with their mouths full.
A.if B.when C.because D.for
4.It was twelve o'clock _______they finished the work.
A.when B.at which C.that D.since
A,B,A,尤其是第二題it是不是做形式賓語,如果選that,那句子要怎么變化呢?第三題為什么不選because和for（for也不是有因?yàn)榈囊馑紗?）第四題為什么不選at which?