The correct option is A one set of chromosomes
The main plant body in bryophytes is haploid gametophyte. Haploid means that the cells of the plant body have one set of chromosomes. When gametes produced from the haploid plant body are fused, a diploid sporophyte is formed which remains attached to the female gametophyte. Diploid means that the cells of the sporophyte have two sets of chromosomes.