In Mendel's experiment, the pure lines refer to plants that are homozygous for a particular trait. This means that they have two identical alleles for that specific trait. Pure lines are essential in Mendel's experiments because when crossed with another pure line that has a different trait, they help determine the pattern of inheritance for that trait.
For example, if Mendel crossed a pure line of plants with yellow seeds (homozygous dominant for seed color) with a pure line of plants with green seeds (homozygous recessive for seed color), all the offspring in the first generation (F1 generation) would have yellow seeds. This is because the yellow seed trait is dominant over the green seed trait.
So, to answer the question:
C. They were homozygous.
