The correct answer is D.
There are two stages of plants' life cycles, these are multi cellular haploid and multi cellular diploid.The gametes typically arise from the gametophyte, which is a muticellular haploid. Fertilization give rise to sporophytes, which is a multicellular diploid. Thus, if gametophyte is n [haploid], then the sporophyte [diploid] will be 2n.