Why are viruses hard to treat?

 Some viruses are hard to treat because  sometimes it’s not the virus that makes us sick; it’s our immune system.

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.

correct answer is a. and d.