Nitrogen is made available in a useful form for animals in the a. fertilizers they absorb. b. plants they eat. c. air they breathe. d. rainwater they drink.

Consider the following planned experiment. factor experimental group control group light exposure tots of sun tots of sun amount of water weekly weekly type of soil nutrient rich nutrient rich size of pot large which variable is being tested in this experiment? small a. size of pot b. type of soil c. light exposure d. amount of water