I believe it is C. as liquid hydrogen.
The fern should be found on the west side of the mountain ranges at higher elevations because the prevailing winds are from the west off the Pacific Ocean so bring moisture in the clouds and as the clouds rise up over the westernmost mountains they cool off and precipitate so in the warm seasons rain would be concentrated in this area and higher up would be cooler.
I would have to say skin or hair
Natural variation provided the phenotypes that natural selection then acted on, over time causing evolution