Summarization：the paragraph is followed by an incomplete phrase or sentence which summarizes the main idea of the paragraph. Spell out the missing letter of the word on your answer sheet.

Most mammals can sprint faster than humans— having four legs gives them the advantage. But when it comes to long distances, humans can outrun almost any animal. Because we cool by sweating rather than panting, we can stay cool at speeds and distances that would overheat other animals.
Human's efficient c system.