A Yeast Strain Was Exposed to Chemical Mutagen

A yeast strain was exposed to chemical mutagen. As expected, exposure to mutagen resulted in a DNA sequence change in an essential gene you examined. Yet this mutation did not result in any lethal phenotype. Which of the following answers would BEST explain this apparent discrepancy?

A) The DNA sequence change occurred in a synonymous nucleotide position of an amino acid and as a result the protein sequence remained unaltered.
B) If the protein sequence was not affected, no lethal phenotype manifested.
C) The DNA sequence change resulted in an amino acid change, but that amino acid change had no negative effect on protein function (i.e., was a neutral change) .
D) The DNA sequence change occurred in a nonsynonymous nucleotide position of an amino acid and as a result the protein sequence remained unaltered.
E) All mutations that cause a change in DNA sequence result in a lethal phenotype.