Answer:
D. The tomato plants in all the fertilized plots
Explanation:
The independent variable in this case is the fertilizer, because it is the one that is changed in this experiment. This is your clue on how to determine the experimental group.
The experimental group is the group the independent variable is applied on. The group that is not subjected to the independent variable is called the control group.
This is done to ensure that the changes in the experimental group was indeed brought about by the independent variable by comparing the difference between the two groups.