Answer:
The correct option will be option D (Gametophyte).
Step-by-step explanation:
Ferns are the seedless, vascular plants belonging to the kingdom Pteridophyta. They are one of the most primitive plant type known and shows alternation of generations in their life cycle.
Both asexual (spores, rhizomes, offsets or stems) and sexual methods of reproduction are known in ferns. Diploid sporophyte undergo meiosis to form haploid spores.
Gametophyte forms a special heart-shaped structure called prothallus below which sex organs are present. Archegonium, the female structure contains a single egg while Antheridium, the male structure, contains flagellated sperms.
thus, option D is the correct answer.