Ron/Stacey please explain the correct usage of "colon:"

[engineer.sunil]

This process resulted in a total of 15 new townships: of which, to date, 7 are still in existence.

(A) of which, to date, 7 are still in existence.
(B) of which number, 7 of the 15 are still, to date, in existence.
(C) of the number 15, 7, to date, are still in existence.
(D) to date of these 15, 7 are still in existence.
(E) to date, 7 of the 15 are still in existence.

Explanation says that "of which" in option A and B do not clearly refer to any antecedent.

Ron/Stacey please explain why "of which" in options A and B is not referring to "15 new townships" ? "of which" is placed adjacent to "15 new townships" in both options A and B

Please explain the correct usage of "colon:"

Source: GMATClub Test

[jnelson0612]

What is the answer for this question?

[mahendru1992]

Sorry for hijacking such an old thread, but I too need an explanation for this question. Why is A not correct?
Btw, E is the correct Answer

[RonPurewal]

"Of which" is perfectly fine here.

(...ah, third-party sources, how we love them)

[RonPurewal]

Also, a colon is nonsense here. A semicolon would be fine, but a colon needs to be followed by something that specifies or explains the previous statement.

Beware of this source.

[RashimaV374]

Ron,

You mentioned that using a semi colon here would have been fine, could you explain why you say this?
If you use a semi-colon the sentence would become - This process resulted in a total of 15 new townships; of which, to date, 7 are still in existence.

Does 'of which, to date..' make for a independent clause? I am aware that a semi colon should separate two independent clauses but often the things i think cannot qualify in fact make for a perfect independent clause, probably this is one such instance, but could you clear that up for me?

I have a similar issue with the word therefore, in many sentences you'll see a ; followed by a therefore - could a sentence starting with a therefore be an independent sentence?

[RonPurewal]

a semicolon would work in choice E. sorry if that was unclear.

[AbhijeetS317]

I doubt a question like this (with these kind of answer choices) would ever appear on the GMAT. In fact this question is not actually reflecting the true usage of a colon in my opinion.

[RonPurewal]

^^
...hence my advice "Beware this source."

may as well lock this thread.