The Process of Somatic Hypermutation of Antibody V Regions Sequences

The process of somatic hypermutation of antibody V regions sequences is initiated by the enzyme AID. This enzyme targets cytidine residues in the DNA sequence that are normally part of a G:C pair in the double-stranded DNA. Yet the hypermutation process generates mutations at both G:C and A:T base pairs of the original sequence because:

A) Following AID action, a double-stranded DNA break plus chewing back of the ends occurs before re-ligation of the sequence.
B) The error-prone polymerase repairs the sequence by inserting random nucleotides.
C) There are two different pathways of repair target, one targeting G:C and one targeting A:T base pairs.
D) B cells are the only cells to express the enzyme uracil-DNA glycoslyase (UNG) .
E) During active transcription both A:T and G:C base pairs are temporarily single-stranded.