Answer:
a. diploid
Step-by-step explanation:
After the fertilization process between haploid egg cell and haploid sperm cell, diploid zygote is formed. Zygote has two sets of chromosomes (one from each gamete) which means it is diploid. Sporophyte stage of life cycle will develop from diploid zygote. During the life cycle of a plant (or algae) sporophyte phase alternates with a gametophyte phase which is haploid. In both, seed plants and flowering plants sporophyte phase (roots, stem, leves, cones/flowers) is more prominent than gametophyte phase (pollen, embryo sac).
Sporophyte phase produces spores via meiosis that develop into gametophte.