问几个小小的语法问题

问几个小小的语法问题
The market for manufactured goods is which economists call "imperfect,"because each company has its own style.这里的which错了么?为什么要改成what?
Even today,through the hustle and bustle of Nevsky prospect,St,Petersburg's main street,the classical beauty of the city mesmerizes the eye.这里的through为什么要改成across呢?意义上有什么不同呢/
In the United States at the time of World War two,when soilders were screened for miliary service the army defined a minimal level of literacy as that was normally achieved in the fifth grade.这里的was normally的was为什么一定要去掉呢?语法道理是什么.
还有请告诉下我什么情况下要用倒装句什么时候用完全什么时候用部分.简单的就好不要粘贴的.(好像说介词开头的时候要倒装吧我记得.还有那个什么not only放开头的.还有类似的什么情况么?)