Answer:
A. If neither parent expresses the trait, but the offspring does, both parents must be heterozygous for the trait.
Explanation:
If neither parents express the trait is because they are heterozygous and the dominant allele is being expressed over the recessive trait. When parents cross they have 25% of having an offspring that expresses the recessive trait, this means the offspring is a recessive homozygous. In the attached example 25% or 1/4 will have a short stem.
