This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
True about Ig gene rearrangement & Ig diversity: 
Select and explain. 
A. Somatic mutations theory, B. DNA rearrangement, C. Appropriate class switching, D. All
D: All
Answer: D: All 
Explanation: A, B, C i.e. Somatic mutations theory, DNA rearrangement, Appropriate class switching