A polypeptide in a wild type microbe contains the sequence Leu-Pro-Tyr-Ser-Pro. A phenotypic variant of the species has the peptide sequence Leu-Pro-Cys-Ser-Pro. This is an example of a(n):.

The mentioned case is an illustration of the missense mutation. A missense mutation is a kind of nonsynonymous substitution, that is, it is a mutation in which a variation in a solitary nucleotide leads to the formation of a codon, which encrypts for a distinct kind of amino acid.  

When a missense mutation takes place within a DNA, a modification in one of the RNA codon sequences results at the time of transcription. This change in codon will ultimately result in the formation of a different amino acid, which gets presented within a protein at the time of translation. Like in the given case, a change in codon resulted in the substitution of the amino acid tyrosine with an amino acid cysteine.  

it is either c or d and i know for sure it is not a or b