Answer:
C) rate of soybean growth
Step-by-step explanation:
In the Cartesian plane, the variable that is placed on the x axis is the independent variable. The independent variable is one that does not need any factor for its existence and determines the changes in the dependent variable. In this case, the independent variable is the amount of fertilizer used in the experiment.
In the same Cartesian plane, the y axis must be occupied by the dependent variable. The dependent variable is the one that depends and is influenced by the independent variable. In the experiment shown in the question above, the amount of fertilizing influences the soybean growth rate, so the soybean growth rate is the dependent variable.