Unlike a scientific theory, a scientific hypothesis describes an observed pattern in nature without attempting to explain it.

volcanoes (an event in the geosphere) release a large amount of particulate matter into the atmosphere. these particles serve as nuclei for the formation of water droplets (hydrosphere). rainfall (hydrosphere) often increases following an eruption, stimulating plant growth (biosphere).

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