verb form

[thanghnvn]

from gmatprep.
pls, justify the use of verb form inhere.

Several educational research groups are denouncing the mayor's proposal of a system by which individual teachers would be given raises or bonuses// should it be that test scores show their students' mastery of reading skills having// improved over a nine-month period.

(A) should it be that test scores show their students' mastery of reading skills having
(B) should it be that test scores show their students' mastery of reading skills have
(C) should test scores showing their students' mastery of reading skills has
(D) if test scores showing their students' mastery of reading skills having
(E) if test scores show that their students' mastery of reading skills has

I do not have oa, but this is definitely from gmatprep.
I think the oa is c, using poe. But "should have done" is used here and I do not understand this usage.

[messi10]

There is already a post for this problem:

several-educational-research-groups-are-denouncing-the-mayor-t3772.html

Please post your question there

Thanks

[jlucero]

Thanks, messi. Let's keep the questions on that thread, so I'll go ahead and lock this thread. Also, the OA here is E. The final verb would be my go-to split here.