Unlike emergency calls that travel through regular telephone lines, where they thus automatically inform the operator of the location and phone number of the caller, cellular calls require emergency operators to determine the location of the caller.

(A) lines, where they thus automatically inform the operator of the location and phone number of the caller, cellular calls require emergency operators to determine the location of the caller
(B) lines and thus automatically inform the operator of the location and phone number of the caller, cellular calls require emergency operators to determine the location of the caller
(C) lines, thus automatically informing the operator of the location and phone number of the caller, the location of the caller on a cellular phone has to be determined by the operator
(D) lines, and thus automatically inform the operator of the location and phone number of the caller, emergency operators have to determine the location of the cellular phone caller
(E) lines, thus automatically informing the operator of the location and phone number of the caller, emergency operators receiving a cellular call have to determine the location of the caller

please explain why each choice is correct/incorrect
from gmat prep

My guess is B, use the 12th's "unlike x, y" construction, use of "where" strange, ambiguous pronoun with "they" can refer to regular telephone lines or emergency calls (two potential plural antecedents)

B. Valid comparison (emergency calls to emergency operators) clearer *fewer pronouns, concise
C. Improper comparison (regular telephone lines to a single location?) Usage Issues "to be" "-ing" yikes!
D. Improper comparison (calls to operators?) but otherwise promising
E. Improper comparison (calls to operators?)

to:gkhan
you are right.OA is "b"

cool, hope it makes sense.

OA is B for 2 reasons

1.Unlike X,Y which is only in A and B2.The usage of where in A is not going back to a location

(A) lines, where they thus automatically inform the operator of the location and phone number of the caller, cellular calls require emergency operators to determine the location of the caller pronoun error
(B) lines and thus automatically inform the operator of the location and phone number of the caller, cellular calls require emergency operators to determine the location of the caller correct
(C) lines, thus automatically informing the operator of the location and phone number of the caller, the location of the caller on a cellular phone has to be determined by the operator wrong comparison [editor: you've misidentified the subject here; the subject of this choice is actually "the location". it's still a nonparallel comparison, though.]
(D) lines, and thus automatically inform the operator of the location and phone number of the caller, emergency operators have to determine the location of the cellular phone caller wrong comparison
(E) lines, thus automatically informing the operator of the location and phone number of the caller, emergency operators receiving a cellular call have to determine the location of the caller wrong comparison
[nice analysis.]

i'll show one possible route of elimination; forum traffic has reached a point where it's not feasible to list everything wrong with a question. if you have further issues with a certain answer choice(s), please go ahead and post them below.


* probably the easiest way to start:
notice the initial comparison
Unlike emergency calls that travel through regular telephone lines

as soon as you see this, you know IMMEDIATELY that the main subject must be parallel to "emergency calls" -- i.e., the main subject must be another type of phone call.

the main subject of (a) and (b) is "cellular calls" --> this is ok.
the main subject of (c) is "the location" --> not ok eliminate (c)
the main subject of (d) and (e) is "emergency operators" --> not ok eliminate (d) and (e)

all that's left is (a) and (b).

in (a):

* you must interpret "where" literally. if you do, then this sentence means that the operator is given the information in the telephone lines (i.e., the operator is literally standing inside the telephone wires). not good.

* we don't know who "they" is.

thus (b)

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Hello, I have a question (about parallel) in choice (B),

Unlike emergency calls that travel through regular telephone lines and thus automatically inform the operator of the location and phone number of the caller,....

Here we have parallel:
"that travel through regular telephone lines" and "(that) thus automatically inform xxxxxx".

I thought the second "that" is omitted, and such kind of omitted structure is confusing to me.

Please tell me if I'm wrong.

Thanks all.

I've found the explanation for my question in other thread:

post25465.html#p25465

Please delete my posts if unnecessary.

Thanks.

no need to delete your posts. thanks for doing some research on your own; there's a lot of good stuff on here!

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Tim Sanders
Manhattan GMAT Instructor

actually, i am wondering is there anything wrong in option C and option E regarding the use of COMMA+verbING construction-->(, thus automatically informing) ??
please help and thanks in advance.

nothing is technically wrong with that construction..

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Tim Sanders
Manhattan GMAT Instructor

Good question and ..
And so well ans. also ..same problem i am faceing right now and when try to find ans got this topic and got the ans. also..
Good ans dear thanks to you all .[spam deleted]

keep your spam off our boards!

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Tim Sanders
Manhattan GMAT Instructor