Hello there! The answer is A trait that helps an organism survive and reproduce in its environment.
An adaptation is something an animal develops naturally to better live in its environment, making A your best option.
It's not B or D because adaptations are the animal's changes, not the environment. It's not C because although how they obtain food may be part of it, it is not the full thing.
I hope this was helpful and answered your question, have a great rest of your day!