Prep07 32题的时态问题

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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
答案E。
可是为什么B不对啊？？解释说had的时代错误为什么呢？
求解！！！！！！！！！！！！！！！！！！！！！！！！！

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