aditya8062 wrote: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


my concern: is option A wrong because "BUT + having been redirected" is not parallel to anything?

One reason to eliminate A is lack of parallelism.
A conjunction such as but must serve to connect PARALLEL FORMS.
In A, but incorrectly serves to connect flowed (verb) to having been redirected (adjective).

In addition to what Mitch has already mentioned above, notice that but is used as a coordinating conjunction in this sentence, and so, must be followed by an independent clause (this is the property of coordinating conjunctions).

But in A, that is not happening.

aditya8062 wrote: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


my concern: is option A wrong because "BUT + having been redirected" is not parallel to anything?

we should focus on the basic grammar and meaning before applying the rules of gmat.
in A, "having directed" show an action prior to "flowed". problematic, not logic
in B, there is no past timeframe, in which "had done " is used. normally "had done" in a sentence needs a past action/time as a mark, but some times we do not have this mark but have time frame in the past. "had done "here have no mark or time frame. wrong
C and D are wrong structurally

normally, in one sc problem, we have 2 choice wrong structurally, which most persons realized and 2 choice wrong meaningly, which the winner realize. gmat still test the basics of grammar but focus more on meaning grammar. meaning grammar , I means, is the grammar which require us to understand the meaning to choose the right pattern. tense problems is meaning grammar because we need to understand meaning to use correct tense. however "they is/they are" is not meaning grammar because we do not need to understand meaning to see that "they is " is wrong.