Morris Is a Big,healthy Bull

Morris is a big,healthy bull.One spring,he fathers ten calves,but five of them are stillborn,their muscles very rigid in a phenotype called "contracture." Farm animals often mate with their close relatives.So,three of the dams (mothers of the stillborns) are also Morris' daughters,and the fourth is his half-sister.The large number of stillborns is most likely due to

A) recessive lethal alleles that occur as new mutations in the doomed offspring.
B) dominant alleles that Morris shares with his mates.
C) multiple lethal alleles that Morris shares with his mates.
D) co-dominance between two lethal alleles.