21. Regarding the seed structure of gymnosperms, what is the origin and ploidy of the "endosperm" that provides nutrients for embryo development?
(A) Produced by double fertilization, triploid (3n)
(B) Developed from maternal sporophyte tissue, diploid (2n)
(C) Developed from female gametophyte tissue, haploid (1n)
(D) Developed from male gametophyte tissue, haploid (1n)

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