The Amino Acid Sequence DAILMNCST Has an S8X Mutation

The amino acid sequence DAILMNCST has an S8X mutation. Which of the following correctly describes this mutation?

A) Seven additional serine residues are inserted next to S.
B) The S is substituted with any amino acid at position 8.
C) There was a frameshift mutation at the S, producing a stop codon.
D) The S at position 8 is mutated to a nonsense codon.