Since you didn’t list the options, I’ll just give you a basic overview, then you can choose the one that fits the best.
Evolution has two primary mechanisms: mutation and natural selection. Mutation causes small variations in an organisms DNA, which can be helpful or hurtful to the organism. Natural selection is the process by which helpful mutations spread through the population because they help the organism survive, and detrimental mutations are removed from the population because they often die before reproducing. Hope this helps!