Heterospory, highly reduced gametophytes, ovules, pollen, seeds are the five adaptations common to all seed plants that ensure their success in the adaptation to land. Three things: The gametophytes of seed plants are reduced and dependent upon the parent sporophyte which protects them (particularly in the case of the female gametophyte). Pollen is covered with sporopollenin which is resistant to physical factors in the environment. The structure of the seed protects the next generation sporophyte and allows it to remain dormant until conditions are right for germination, development and growth.
Vascular plants reproduce with seeds, nonvascular plants do not, therefore it is C.
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