___________ divides mitotically to form male gametes.

The correct option is B Generative cell
Pollen mother cell (PMC) undergoes meiosis to form four haploid microspores. These microspores develop into the male gametophytes - pollen grains.
Each pollen grain divides mitotically to form two cells, a large vegetative cell and small generative cell. The generative cell divides by mitosis and produces two male gametes.