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
Mutations are due to changes in: 
Select and explain. 
A. DNA nucleotide sequence, B. RNA nucleotide sequence, C. Amino acid sequence of ribonuclease, D. Cell walls
A: DNA nucleotide sequence
Answer: A: DNA nucleotide sequence 
Explanation: None