1. ___ their economic situations, they got some relief fund from the government.
　　a. Considering b. Considered
　　c. Having been considered d. Being considered
答案是a ,为什么其他的选项不可以?
2　___,he could not lift the heavy stone.　　
a. Strong as he was b. So strong was he
c. He was strong enough d. As he was strong
为什么a不可以?
3.It was May ___we met each other in the park .　　a. when b. that c. which d. since .
4. Those are the circumstances ___ it was impossible for us to continue the experiment any longer.
　　a. why b. how c. what d. where
5.　The girl ___forward to buying a new dress.
　　a. referred to look b. refers to looking
　　c. referred to looks d. referring to look
以上各题,请详细叙述一下思考过程,谢谢!

１.Ｃonsidering　sth，已经成为一个固定句型了，考虑到．．．，就．．．而言
２.不是选Ａ吗？晕～～可能是因为前后是转折关系吧
３.Ａ．定语从句～先行词是Ｍay，从句不缺成分，所以用when来引导，如果Ｍay前面有个in的话，就应该选that，变成强调句．但是本句不属于那种情况
４.Ｄ．和situation的情况一样，遇到这种句子，先行词是表形式情况的，在从句不缺成分的时候，都用where
５.Ｃ．referred　to前面省略了who　was．referred　to做定语修饰girl，把它省略不看，就是：The girl (who was referred to )looks forward to buying a new dress.分清成分句子就简单了～