Most Vaccines Cause the Formation of Antibodies Against a Particular

Most vaccines cause the formation of antibodies against a particular pathogen, but if the pathogen mutates quickly, the vaccines don't stay effective. How does the vaccine against diphtheria work that avoids this problem?

A) Diphtheria doesn't mutate quickly, so the vaccine works for awhile.
B) The vaccine only works against the diphtheria that produces toxins.
C) Because the vaccine works against the toxin produced, not the bacteria cell itself, mutations to the cell don't alter the vaccine's effectiveness.
D) The vaccine works against the bacteria cells directly, so they don't have time to mutate.
E) The vaccine is naturally selected for, so it adjusts to the mutations in the bacteria.