0. The word "biorhythms" in paragraph 7 is made up of a prefix and a root word. Bio- is a Greek prefix meaning "one's life or way of living." Which word or phrase from the rest of paragraph 7 helps you to understand the meaning of the root word rhythm? A "main challenge . . . is sleeping" ® "phase with day and night" © "work 18-hour days" • "isn't any natural light"