All Five of the Children in a Family Were Born

All five of the children in a family were born with a genetic disorder. The disorder is inherited as autosomal dominant. If this is not a statistical rarity, the likelihood would be that:

A) One parent has both chromosomes with the affected gene.
B) Both parents are carriers.
C) One parent is a carrier and the other parent is unaffected.
D) One parent has one chromosome affected and the other parent has none.