The correct option is D Gametes, zygote, embryo, seed
The formation of gametes is the first step in reproduction in flowers.
Male gametes are found inside tiny pollen grains on the anthers of flowers. Female gametes are found in ovules of a flower.
The union of these two gametes takes place which results in the formation of a zygote.
So, after fertilization, the ovule contains a diploid zygote and then cell division begins and forms the embryo of the next sporophyte generation.
Seeds then develop from the ovules in the female part that has been fertilized by the pollen from the male parent plant.
Thus, the correct answer is option (D), 'Gametes, zygote, embryo, seed'.