Control (or reduced "noise") is important for a well designed experiment. Which aspect of the following experiment demonstrates control? Explain your answer.
A. Cyanogenic and acyanogenic clover plants are grown in a neutral greenhouse environment with equivalent light, water, and nutrients provided.
B. Both types of clover plants are grown under three different Nitrogen fertilizer treatments that reflect differences in urban vs. rural environments.
C. The number of plant (dependent variable) and compared between the two groups (cyanogenic plants vs. acyanogenic plants) and also across the three treatments (independent variables).