Sporophytes are?

a. Gametes

b. zygotes

c. haploid

d. diploid

Sporophytes are diploid because diploid is a sporophytes.

It's D. diploid

in the life cycle of plants with alternating generations) the asexual and usually diploid phase, producing spores from which the gametophyte arises. It is the dominant form in vascular plants, e. g., the frond of a fern.