Hi aditya8062,

You are correct, the answer is C. I'll get to your specific questions shortly, but first let's look at how the incorrect answers can be eliminated.

"...making the construction industry's economic health much more robust than it was five years ago"

We need "it was" in the above phrase to make the comparison correct: the economic health today compared with the economic health five years ago. Thus we can eliminate answers A, B, and D. We can eliminate answer E because it unnecessarily uses the preposition "in."

Yes, "it was" refers to the construction industry's economic health.
No, your sentence "making the construction industry's economic health much more robust than construction industry's economic health was five years ago" is not correct. Here it is again, made technically correct (but awkward and not the preferred answer because it avoids using a pronoun and is too long):

"making the construction industry's economic health much more robust than the construction industry's economic health was five years ago"

For reasons noted above, we do need the "it was" to keep the right sentence structure.

Thanks for your reply

but my question is still open as:

i fail to understand as what is parallel to "it was"

any construction after "than"/"as" in the form of "it was" has to be parallel to some "to be" form that appears before "than/as" . how do i reconcile this?

ALSO

you said: No, your sentence "making the construction industry's economic health much more robust than construction industry's economic health was five years ago" is not correct. Here it is again, made technically correct (but awkward and not the preferred answer because it avoids using a pronoun and is too long):

but unfortunately my sentence was not this .my sentence was: making the construction industry's economic health much more robust NOW than five years ago---->i am comparing the "construction industry's economic health" in two time periods viz "NOW" AND "FIVE YEARS AGO"

Hi again,

I think I understand what you are asking, thank you for clarifying.

We need parallelism in singular forms of noun and pronoun ("construction industry" is the singular noun, and "it" is the singular pronoun). My point is that we need the "it" in "it was" to be correct.

Your sentence with "now" still needs the "it was" to be correct. The VERB + ing at the starting of the clause ("making") is functioning as the present tense "to be" that is later contrasted with "it was."