A scientist wants to determine which fertilizer is more effective—fertilizer X or fertilizer Y. The best way for her to proceed would be to design an experiment with
a) Two groups of plants—a group fertilized by Y and a control group with no fertilizer.
b) Two groups of plants—a group fertilized by X and a control group with no fertilizer.
c) Three groups of plants—a group fertilized by X, a group fertilized by both X and Y, and a control group with no fertilizer.
d) Three groups of plants—a group fertilized by X, a group fertilized by Y, and a control group with no fertilizer.