Explain how is it possible to have thousands of different proteins when there are only a 20 different amino acids

explanation:

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.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."