Unlike emergency calls that travel through regular telephone

[RonPurewal]

there are no such rules based on the presence/absence of commas. https://www.manhattanprep.com/gmat/foru ... tml#p59386

[RonPurewal]

moreover, the presence/absence of commas is not tested on this exam, in any way whatsoever.

if you find yourself thinking about "sentence with comma vs. sentence without comma"—EVER—immediately drop that train of thought, and consider other aspects of the sentence.

[qianruS779]

OK, Thank you for your info.

Best, Song

[RonPurewal]

you're welcome.

[ZoeZ42]

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)

Hi Ron,

as you said above, operators can not get info from wires inside, that means telephone line can not inform operators , so the pronoun "they" couldn't refer to telephone lines, thus, "they" refers to "emergency calls", right?

thanks a lot
have a nice day

>_~

[RonPurewal]

you could argue that case, sure.

regardless, "where" is clearly and plainly wrong, so you should have little trouble getting rid of (a) anyway.