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
One of the following mutation is potentially lethal - 
Select and explain. 
A. Substitution of adenine for cytosine, B. Substitution of methylcytosine for cytosine, C. Substitution of guanine for cytocine, D. Inseion of one base
D: Inseion of one base
Answer: D: Inseion of one base 
Explanation: D i.e. Inseion of one base