Johannes wants to know whether soil, water, or both are needed for plant growth. he chooses to conduct experiments on a willow tree for five years to answer his question. how can his experimental methods be changed to improve his experiment?

Johannes wants to know whether soil, water, or both are needed for plant growth. He chooses to conduct experiments on a willow tree for five years to answer his question. His experimental methods can be changed by testing more factors in the environment. This will improve his experiment.

I hope it helps, Regards.

i believe the answer would be b. hope it : )