As you move down a group, atomic radius increases
I think the correct answer would be C. It would be restricting water and/or nutrients, instead of supplying ample quantities of both that would not change the results of the experiment. This is because you are still supplying the same amount of nutrients and other things needed by the plant so the ratio of the growth of the plants will still be the same.
Explanation:
Porosity depends on the size, shape, and mixture of grains and particles that compose soil and rock. For instance, small particles such as clays can compact more closely together, reducing the amount of porosity. However, larger particles such as sand and gravel will have more spaces available between them.