this sentence was not easy for me. so please excuse me in case if my analysis is not convincing
Retailers reported moderate gains in their November sales, as much because
of their sales of a year earlier being so bad as that shoppers were getting a head start on buying their holiday gifts.
(A)
of their sales of a year earlier
being so bad as that - "because of their sales" is incorrect....."being so bad" is incorrect too
(B)
of their sales a year earlier
having been as bad as because - "because of their sales" is incorrect......"having been" is wrong because we need past perfect tense
(C)
of their sales a year earlier
being as bad as because - "because of their sales" is incorrect....."being as bad as" is wrong and there is no comparison
(D)
their sales a year earlier
had been so bad as
because - "their sales" is correct......"had been" is correct because the sentence says sales a year earlier we need past perfect tense....because their sales is parallel with because shoppers
(E) their sales of a year earlier
were as bad as
that - "their sales" is correct...... we need "had been" is correct because the sentence says sales a year earlier we need past perfect tense and not "were"...."as bad as that" is incorrect