You could say variation in offspring (so cloning things they basically just multiple the exact same thing but with reproduction, whatever is made differs a little bit or a lot from its "parents"
again temperature, it occnaturally and when you do things like run or play you get hotter and sweaty ya'know.
I think the answer would be C) There is a problem with overfishing. Ban fishing for large fish so their size and population can recover, but allow the fisherman to take smaller fish.
banning fishing all together or ignoring the problem would definitely not work and bringing in a new species could disrupt the ecosystem and cause more of an issue.