Detailed Instructions: You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.
Problem:Edith's checkerspot butterfly is a non-migratory species found in distinct populations from Canada to Mexico. Today, populations in southern regions are declining while new populations push the northern limit further north. This range shift provides evidence for the theory of
(A) mass extinction. (B) global warming. (C) gene dominance. (D) natural selection.
Solution:
B