What process allows for me to development of haploid sex cells?

Meiosis is a process that are responsible for the production of haploid sex cells.

Explanation:

Meiosis is a type of cell division in which a single parent cell is divided into four daughter cells. Each daughter cell are haploid i. e. half number of chromosome are present. In meiosis 1, two cells are produced having diploid cells while in meiosis 2, the two daughter cells again divided into four daughter cells having half number of chromosome.

if your own plato the answer is b. the fern transitioned from sporophyte generation to gametophyte generation.