(Choices A and C) Missense mutations are single base substitutions that result in the placement of an incorrect amino acid in a protein sequence. These mutations occur within the coding region of a gene and do not alter protein length. A conservative mutation is a type of missense mutation where an amino acid is replaced with another that has similar biochemical characteristics. Conservative mutations generally preserve protein function unless the mutation occurs in a critical region (eg, active site of enzyme).
(Choice D) Nonsense mutations introduce a premature stop codon in a coding region, resulting in the production of a truncated protein. The mutation described is not a nonsense mutation because it was caused by a single base deletion (not a base substitution).
(Choice E) A silent mutation is a single base substitution within a codon that does not change the amino acid (due to codon redundancy). Silent mutations have no effect on protein formation or function.