语法问题，XDJM帮帮我吧？？？

1,(Unlike most warbler species, the male and female blue-winged warbler are very difficult to tell apart)
B Unlike most warbler species, the gender of the blue-winged warbler is very difficult to distinguish.
C Unlike those in most warbler species, the male and female blue-winged warblers are very difficult to distinguish.
D It is very difficult , unlike in most warbler species, to tell the male and female blue-winged warbler apart.
E Blue-winged warblers are unlike most species of warbler in that it is very difficult to tell the male and female apart.
答案是E。我不知道为什么D不对。

2，(For all his professed disdain of such activities ), Auden was an inveterate literary gossip.
B Having always professed disdain for such activities.
答案是A。我觉得题目中应该有“虽然，但是”的意思，但是A中的FOR没有，为什么选A而不选B。

3，Building large new hospitals in the bistate area would constitute a wasteful use of resources, (on the basis of avoidance of duplicated facilities alone.)
A on the basis of avoidance of duplicated facilities alone
B on the grounds of avoiding duplicated facilities alone
C solely in that duplicated facilities should be avoided
D while the duplication of facilities should be avoided
E if only because the duplication of facilities should be avoided
答案是E，为什么A，C不对。E中的if only because 是什么意思。

4，Freedman’s survey showed that people living in small towns and rural areas consider themselves (no happier than do people living )in big cities.
E not as happy as are people who live
答案是A。这里A中的do 指代的是consider吗？如果是，句子意思就变成了“不比people living in big cities 认为得更快乐”。我自己感觉这里句子意思应该是“不比people living in big cities更快乐”，因此，我觉得比较从句中应该用are.请教各位。

5,In the middle-1920’s the Hawthorne works of the western Electric Company was the scene of an intensive series of experiments (that would investigate changes in working conditions as to their effects on workers’ performance.)
B investigating the effects that changes in working conditions would have on workers’ performance
C for investigating what are the effects in workers’ performance that changes in working conditions would cause
D that investigated changes in working conditions’ effects on workers’ performance
E to investigate what the effects changes in working conditions would have on workers’ performance
答案是B，这题E为什么不对？？？不定式作后置定语也完全说得通啊。