Answer:
A. The fern transitioned from gametophyte generation to sporophyte generation.
Explanation:
Ferns undergo an ALTERNATION of GENERATIONS in their reproductive life cycle. That is, they alternate between an incospicuous gametophytic stage and a dominant sporophytic stage. The sporophyte produces haploid spores, which germinates into the gametophyte plant called PROTHALLUS.
The gametophyte produces gametes (male and female) which fuse together to form the diploid zygote, which eventually develops into the SPOROPHYTE plant via mitosis. In this question, the brown dots from the underside of a fern's leaves that Maria collected are the spores.
When she places them in a pot, the spores germinated into gametophyte stage, then formed sporophyte, which is the small leaves she noticed growing from the pot. From this, it can be observed that the fern is transitioning from GAMETOPHYTE generation to SPOROPHYTE generation.
