true breeding plant means plant which produces same as their parent plant and alleles for these type of organisms are homozygous, True-breeding plants and organisms may express phenotypes that are either homozygous dominant or homozygous recessive. With complete dominance inheritance, dominant phenotypes are expressed and recessive phenotypes are masked in heterozygous individuals, means if true breeding plant is with wrinkled seeds then its progeny will also produce only wrinkle seeds, same in the case of dominant one.
and only option c) is showing the characteristic of true breeding plants.