When Is a Single Base Substitution in DNA Least Likely

When is a single base substitution in DNA least likely to be deleterious?

A) When a stop codon results
B) When the codon that results specifies the same amino acid as the original codon
C) When the amino acid substitution alters the tertiary structure of the protein
D) When the amino acid substitution at the active site of an enzyme
E) When a new start codon is inserted