A Child Is Born with a Lethal Dominant Allele

A child is born with a lethal dominant allele. This would seem to be impossible since either parent, had they possessed this allele, would have suffered its lethal effects. What is a possible explanation?

A) The child's allele is a spontaneous mutation that neither parent had to deal with.
B) The allele could have varying expressivity and not always be lethal.
C) The allele could have delayed onset.
D) All of these are possible.
E) None of these is possible.