To make life simple, before we embark on solving this question, just dump C and E for being blatant fragments. We can also drop D for using two back-to-back subordinate clauses with just a main clause. In addition, the use of 'because' and 'since' in the same sentence is awkward.
A prickly observation giving a serious doubt whether GMAT is oblivious of this norm is that in A and B which are complex sentences, the comma shouldn't have been used when the subordinate clause follows the main clause.
Notwithstanding
...
A prickly observation giving a serious doubt whether GMAT is oblivious of this norm is that in A and B which are complex sentences, the comma shouldn't have been used when the subordinate clause follows the main clause.
Notwithstanding
...
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