The correct option is C Three - celled
Pollen grain is the first cell of the gametophyte. The microspore germinates in situ i.e., while within the microsporangium. Each microspore divides asymmetrically into a 2-cells: a smaller prothallial cell and a larger antheridialcell. The prothallial cell does not divide further while the antheridial cell divides into a smaller generative cell near the prothallial cell and a larger tube cell. Finally pollination takes place at 3-celled stage.