Two plants are crossed, resulting in offspring with a 1:1 phenotype ratio for a particular trait. This suggests _____.
A. that one parent is heterozygous and the other is a homozygous recessive
B. incomplete dominance
C. that the parents were true-breeding for contrasting traits
D. that the parents were both heterozygous
E. that one parent is heterozygous and the other is homozygous dominant