How Might a Single Base Substitution in the Sequence of a Gene

Multiple Choice

How might a single base substitution in the sequence of a gene affect the amino acid sequence of a protein encoded by the gene,and why?

A) Only a single amino acid could change,because the reading frame is unaffected.
B) The amino acid sequence would be substantially altered,because the reading frame would change with a single base substitution.
C) All amino acids following the substitution would be affected,because the reading frame would be shifted.
D) It is not possible for a single base substitution to affect protein structure,because each codon is three bases long.