Indicate Whether Each of the Following Descriptions Better Applies to Class

Short Answer

Indicate whether each of the following descriptions better applies to class switching (C), somatic hypermutation (S), or both (B). Your answer would be a four-letter string composed of letters B, C, and S only, e.g. SSSB.
( ) It is dependent on activation-induced cytidine deaminase.
( ) It involves sequence changes in the CH domains only.
( ) It increases the affinity of antibody-antigen binding.
( ) It takes place in germinal centers after antigen stimulation.