b. Producing gametes (sperm and egg cells) that unite inside the female reproductive system.
Explanation:
The "gametes" refer to the sex cells in humans. The female sex cells are called "egg cells" and these are being produced by the <em>ovary</em>. The male sex cells are called "sperm cells" and these are being produced by the<em> testicles.</em> After copulation, there's a probability for the egg cells and sperm cells to unite. They unite inside the female's reproductive system, specifically inside the <em>"fallopian tube."</em>
