Answer: A. k
Step-by-step explanation:
The explanatory variable is a type of independent variable. The explanatory variable explains changes in the response variable. Thus, the response variable is dependent on it. Normally, independent variables are plotted on the horizontal axis. In that case, the response variable would be plotted on the vertical axis.
In this scenario, k is the explanatory variable and i is the corresponding response variable. Thus, the correct option is
A. k