Answer: A. the result of an experiment.
The experimental group and treatment group are the same group. It's just two different names for the same thing. If you apply a treatment to a group, then that's where you're performing the experiment.
For instance, if you are testing a fertilizer, then the independent variable would be "use of fertilizer or not using fertilizer". So that means the control group doesn't get any fertilizer. The dependent variable would be the heights of the plants between the two groups, so we can see if the fertilizer has an effect or not. This is the result of the experiment. So in other words, the input is the fertilizer (or no fertilizer), and the output is measuring the heights of the plants. The output is the result we analyze.
Keep in mind that the heights of the plants are likely to be randomly distributed. So this is where statistics comes into play. If the plants grow due to some random chance, and not necessarily the fertilizer, then you can use the control group to determine if that's the case or not. The control group helps you do this comparison.
As the name implies, "dependent" means it relies on something else. The height of the plant relies on if you used fertilizer or not. The independent variable is able to change without relying on any other variable.