A green-seeded pea plant and a yellow-seeded pea plant have offspring with all yellow seeds. What is the most likely reason?

The most likely reason for the offspring of a green-seeded pea plant and a yellow-seeded pea plant having all yellow seeds is:

C. The genes from the yellow-seeded parent were dominant.

In pea plants, yellow seed color is typically a dominant trait over green seed color. When a yellow-seeded plant (homozygous dominant, YY, or heterozygous, Yy) is crossed with a green-seeded plant (homozygous recessive, yy), the offspring will all display the dominant phenotype, which is yellow seeds.