Final answer:
Evolution by natural selection is a fact. Thus, this correct option is a-true.
Step-by-step explanation:
The statement is True. Evolution by natural selection is indeed a fact. Natural selection is a major mechanism of evolution, where it acts on phenotypic variations in populations. It is a force that makes animals adapt to fit their environment, leading to changes in the characteristics of living things over time. This theory is supported by scientific evidence from many disciplines, including biology and mathematics.