Answer:
A. all yellow
Step-by-step explanation:
As we know that, a true breeding plant for a certain trait means that both the alleles of a gene are same and the plant is homozygous for the trait. So it means that a true-breeding plant with yellow seeds will have alleles as YY. While, true-breeding plant with green seeds will ave alleles as gg.
Lets see what happens when we cross them.
P1: YY x gg
Gametes: Y : Y g: g
Offspring: Yg: Yg: Y:g :Yg
So the genotype of all the offspring is Yg, and because yellow is dominant over green (stated in the question) .
Consequently all the plants will have yellow seeds.
Hope it helps!