Form a hypothesis about how a population of dandelion plants might be affected by a population of rabbits

A hypothesis is the proposed explanation which is subject to be proved by the experiment by scientific method. Hypothesis is not a wild guess but based on prior study or explanation.

Rabbits are only depended on the dandelion plants which will decrease the population of dandelion plants over time which negatively impacts on rabbit population too by decreasing.

Thus, the correct answer would be -  if the rabbit's population increase, then dandelion plants will decrease over time.

The answer to your question is D. To create the full picture of evolution, and how the species that exist on our planet came to exist in their current forms, it is important to take in information from all the possible fields of science including biology, chemistry and geology.