Variation occurs [before/after changes to the environment.​

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.

thinking it would be d not too sure but i think it's right

meiosis is the first to occur after the nuclei of opposite of opposite mating types fuse

a chain link fence because there so tiny even my albino donkey can't get out