I believe D. because all the organisms that live in a lake can be a bunch of living things that would be considered a population and not a species. I canceled out B. from the get go because, I don’t believe non living organisms can be in a population ?
Please get back to me if I’m right or wrong :)
Answer:
The substance with a weaker molecular attraction
If there weren't any predators, the population of prey would increase and they would starve due to too many mouths to feed.