Answer:
The correct answer is - the theory.
Explanation:
A theory is a explanation which is tested by all different experiments by the independently. It is like a fact or well substantiated explanation. It is not a guess as it always supported by the evidences acquired by scientific method over course of the time.
The evolution by natural selection is a theory is it is not proven wrong or false and is supported by well substantiated explanations.
Thus, the correct answer is - A theory.
