The Reason That the HD Allele Acts as a Dominant

The reason that the HD allele acts as a dominant allele is

A) The mutant HD allele suppress protein production from the normal HD allele
B) The HD mutation results in a protein that can damage nerve cells even in the presence of the normal protein
C) The normal HD allele does not normally produce a protein but the mutant HD allele does
D) The protein produced from the mutant HD allele is non-functional