The answer is none of the above
I think it’s C but not precisely sure about it
Answer: D. Plants do not eat, so both chloroplasts and mitochondria are needed to make enough energy for plants to grow.
Explanation: Option A is invalid since plant cells do use ATP. Option B is invalid since animal cells don't make their energy with chloroplasts. Option D is the most realistic one since chloroplasts in the plant are the ones that make the food for the plants, plant doesn't have a "mouth" so they depend on chloroplast to make food.
The keystone species is the one at the bottom of the pyramid, if we look at it like a pyramid. If the grass dies, then the deer cannot get food and die, and the predator cannot eat and dies, and the whole ecosystem can fall apart.