Cystic fibrosis is an autosomal (not sex-linked)recessive trait.It mostly affects the lungs,and long term issues include frequent lung infections.A man and woman are healthy,and neither have cystic fibrosis,but they have one child out of four who has cystic fibrosis.What are the genotypes of the child's parents?

A)One parent must be homozygous for the recessive allele; the other parent can be homozygous dominant, homozygous recessive, or heterozygous.
B)One parent must be heterozygous; the other parent can be homozygous dominant, homozygous recessive, or heterozygous.
C)Both parents must be heterozygous.
D)One parent must be homozygous dominant; the other parent must be heterozygous.
E)Both parents must be homozygous dominant.