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.