Sun is the main source of light for the plants to function photosynthesis
The variable that is intentionally manipulated or changed in a controlled experiment is know as the B) Independent Variable.
This is done, as the question states, to test the hypothesis. In other words, it is changed in order to see what results are produced, then the results are analyzed, and ideally an explanation of the changing results will arise and progress can be made in the experiment.
Based on the graph, you can see that the population of grass is high, which indicates that the one that feeds on them has been affected. Logically, the rabbits are those that feed on it and as you can see, their population has lowered, and so did the snakes and the hawk.
So among the choices, B. a disease in the population of rabbits may have lead to the graph shown.
In my opinion evolution is a myth but the answer is yes