Concept:A pollen grain is the male gametophyte of a flowering plant and forms the male gametes needed for fertilization.
Explanation:The pollen grain contains a generative cell.
Before fertilization, this generative cell undergoes mitosis.
Mitosis produces two identical male gametes, also called sperm cells.
These two gametes are essential for double fertilization in flowering plants.
One gamete fuses with the egg cell, while the other fuses with the polar nuclei.
Therefore, each mature pollen grain produces exactly two gametes before fertilization.
Answer:B. two