In making gametes, what type of cell division (mitosis/meiosis) does a gametophyte use?

The correct answer will be mitosis.

Explanation:

The life cycle of a plant is divided into two phases - diploid sporophyte and haploid gametophyte.

The gametophyte produces haploid gametes through a process of cell division which can produce daughter cells with the same genetic material without changing the ploidy that haploid cells will produce haploid cells. The equational type of cell division is known "mitosis" which produces cells with the same ploidy.

Hence, gametophyte (haploid) → gametes (haploid) through mitosis and thus option mitosis is the correct answer.