How do spores help sustain the population of ferns?

Ferns are plants that do not have flowers. Ferns generally reproduce by producing spores. Similar to flowering plants, ferns have roots, stems and leaves. However, unlike flowering plants, ferns do not have flowers or seeds; instead, they usually reproduce sexually by tiny spores or sometimes can reproduce vegetatively, as exemplified by the walking fern.

Their type of life cycle, dependent upon spores for dispersal, long preceded the seed-plant life cycle. Because of their ability to disperse by spores and their capacity to produce both sex organs on the same gametophyte and thus to self-fertilize, it is said that ferns possess higher powers of long-distance dispersal and establishment than do seed plants.

i believe the correct answer is d

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