D On May 23,1989, Stefania Follini came out from a cave at Carlsbad , New Mexico. She hadn’t seen the sun for eighteen and a half weeks . Stefania was in a research program, and the scientists in the program were studying body rhythms (节奏)。In this experiment Stefania had spent 130 days in a cave ,30 feet in depth.During her time in the cave, Stefania had been completely alone except for two white mice. Her living place had been very comfortable ,but there had been nothing to fell her the time .she’d had no clock or watches , no television or tadio. There had been NO natural light and the temperature had always been kept at 21℃Stefania stayed in the cave for a long time because___________.

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