The international report showed that American science students did as well, if not better than, their counterparts in other cultures.
(A) as well, if not better than
(B) as well as, if not better than
(C) just as well, whether or not better than
(D) just as well if not better as
(E) as well, and perhaps better, as
B - correct.
remaining all idiomatically incorrect.
Balvinder, one suggestion... go through idiom list once so that you can crack these questions very fast.