Cells divide in a sequence of specific stages called the

Cells on the path to cell division proceed through a series of precisely timed and carefully regulated stages. In Eukaryotas, the cell cycle consists of a long preparatory period, called inter phase. Inter phase is divided into G1, S, and G2 phases.

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