Which pair of events would directly result in a constant number of chromosomes in body cells from one generation to the next in sexually reproducing species?

Meiosis and fertilization

Explanation:

The type of cell division that takes place in the sexually reproducing cells in meiosis.

Meiosis is the type of cell division which maintains the ploidy level in the new organism by forming cells with haploid or half the number of chromosomes.

The meiosis produces 4 haploid gamete cells which when fuses or fertilise with the gamete cell of the opposite sex again form a diploid organism. This type of cell division maintains a constant number of chromosomes.

Thus, meiosis and fertilisation are correct.