Which describes a constant in an experiment?
a. the variable changed by the experimenter
b. the quantity that must remain the same
d. the variable that changes in response to the experiment
d. the statement that is worded to test the experiment

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.