IMO E
OA?

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
B. of their sales a year earlier having been as bad as because
C. of their sales a year earlier being as bad as because
D. their sales a year earlier had been so bad as because
E. their sales of a year earlier were as bad as that

This is a classical parallelism problem
AS much X AS Y
Aas much because of their sales of a year earlier being so bad as that shoppers
Bas much because of their sales a year earlier having been as bad as Cbecause shoppers were getting a head start
as much because of their sales a year earlier being as bad as because shoppers were
D their sales a year earlier had been so bad as because
E as much because their sales of a year earlier were as bad as that

Hope this helps!!!