Sentence Correction

Byron possessed powers of observation that would have made him a great anthropologist and that makes his letters as a group the rival of the best novels of the time.
A) makes his letters as a group the rival of
B) makes his letters as a group one to rival
C) makes his letters a group rivaling
D) make his letters as a group the rival of
E) make his letters a group which is the rival of

IMO D

............powers.................make (abc out)
here which must be preceded by a comma,also comparing "a group" to "the best novels", which is no good pick D