The correct option is D meiosis to form haploid spores.
In organism with haplontic life cycle, the zygote divides by meiosis to form haploid spores. In haplointic life cycle, the dominant stage is the haploid gametophyte. The sporophyte is represented by the diploid zygote. The zygote divides meiotically to form haploid spores, which undergo mitosis to form multicellular haploid organisms. Diploid stage is not free-living. Examples : Green algae like Volvox, Spirogyra, Chlamydomonas, etc.