各路神仙看过来。。。PREP07-Q32

情未浓

The Chicago and Calumet Rivers originally flowed into the St. Lawrence by way of Lake Michigan,but having been redirected by constructing canals so that the water now empties into the
Mississippi by way of the Illinois River.

(A) Rivers originally flowed into the St. Lawrence by way of Lake Michigan, but having been redirected by constructing

(B) Rivers had originally flowed into the St. Lawrence by way of Lake Michigan, but they have been redirected by constructing

(C) Rivers, which originally flowed into the St. Lawrence by way of Lake Michigan but have been redirected by the construction of
(D) Rivers, originally flowing into the St. Lawrence by way of Lake Michigan, but having been redirected by the construction of
(E) Rivers, originally flowing into the St. Lawrence by way of Lake Michigan, have been redirected through the construction of

OA：E

我的问题是：选项B的解释说不能用过去完成时。但是另一个PREP的正确句子是：
Ozone, a special form of oxygen that screens out harmful UV rays, reaches high concentrations twelve miles above Earth, where it had long appeared immune to human influence; we have now realized, though, that emissions of industrial chloroflorocarbons deplete the ozone layer.
为什么上面这里需要用过去完成时来突出对比，而上题中B选项用过去完成时确实错的？

求各路神仙指教啊！

HarrisZheng

B选项还有一个错误是by constructing
rivers是不可能作为constructing的动作发出者的
严格来说 B选项的过去完成时部分语法上也可以成立 但没有强时间对比的情况下 慎用过去完成时
另一方面 GMAC决不会把B选项改写成
Rivers had originally flowed into the St. Lawrence by way of Lake Michigan, but they have been redirected through the construction of
通常来讲 错误选项 都有一个以上的点可供排除 所以 不必太钻牛角了
再往大了说 任何语言都是博大精深并且不断变化着 所以 没有绝对的教条

情未浓

我知道B还有by constructing这个错误。
我提这个问题也只是希望更好地理解过去完成时的一些用法。不把正确的选项错误地排除，也更有效率地排除错误选项。