One of the following mutation is potentially lethal: (A) Substitution of adenine for cytosine, (B) Substitution of methylcytosine for cytosine, (C) Substitution of guanine for cytosine, (D) Insertion of one base
Answer is D. Insertion of one base causes frame shift mutation. This result in production of garbled protein (protein with completely different AA sequence). So, this can be lethal.