Some combinations of recessive alleles cause problems so severe that the fetus ceases to develop.Such lethal allele combinations appear to alter Mendelian ratios because

A) the allele is masked in heterozygotes.
B) carriers do not constitute a progeny class.
C) they do not show a 1:2:1 genotypic ratio.
D) homozygotes for the lethal allele do not appear as a progeny class.
E) homozygotes for the lethal allele pass it on to half their offspring.