Answer:
The correct answer is a: The community was under top-down control
Step-by-step explanation:
Top-down control refers to scenarios where superior predators control the structure and dynamic of an ecosystem. These systems are affected by the presence/absence of the superior predator influences all the lower links in the trophic chain.
In the exposed example wolves, that are considered to be the top predators, affected the white-tailed deer populations being the cause of its decrease. As wolves used to feed on white-tailed deer, they kept these populations under control, but once the wolves got extinct, the deer population increased again. Probably, this explosion in the deer´s population also affected its lower link in the trophic chain.