In humans, a single gene with two alleles controls the shape of the earlobe. There is a free (unattached) allele and an attached allele (see the diagram below). The genetics of the earlobe have been determined, and it turns out the free allele is dominant to the attached allele.

If a woman who is heterozygous for free earlobes has children with a man who is also heterozygous for free earlobes, what is the probability that they will have a child with free earlobes?

A. 100%
B. 25%
C. 75%
D. 50%