Available choices:
[A]. environment;
[B]. mutations;
[C]. competition;
[D]. relocation;
[E]. Darwin;
[F]. evolutionary development;
[G]. root growth;
[H]. research;
Given those answer options, answer the question: Fact 1: Mutations are essential for evolution to occur. Fact 2: Natural selection is the mechanism of evolution. Given the two facts above, what enables natural selection to occur?
A:
[B].