1.Why haven't you accomplished your tasks yet?
You( )to finish them last Friday.
A.were supposed B.are supposed C.are supposing D.were supposeing
2.-Obama won the election.It's amazing!
-Yes.But the result was within ( )we had expected,( )brought great joy to many young people and the black.
A.that;which B.that;that C.what;what D.what;which
3.The robber had escaped and was nowhere to be found when the polic( ).
A.arrive B.arrived C.have arrived D.had arrived
4.It can't be a(n）（ ）that four jewelry stores were robbed in one night.
A.coincidence B.accident C.incident D.chance
正确答案分别为A,D,B，A。拜托大家帮忙看一下

1、be supposed to 是应该, 被期望的意思，由于时间状语是last Friday，未确定的过去时，所以是：A；
2、第一空what为the thing which之意，（the thing ）既作within的介词宾语（which）又作expected的逻辑宾语；第二空which作brought主语。所以是：D；
3、本句是个过去完成时的时间状语从句，主句是过去完成时，从句就应是过去式。所以是过去时：B.arrived ；
4、是个词语理解题，要知道每个词的具体含义，coincidence是 同时发生或同时存在(尤指偶然)的事；accident为 意外事件, 事故；incident为 事件, 事变；chance为机会, 可能性, 偶然性，虽也有偶然性之意，但抽象意义更重些。所以：A更贴切。