TOEFL Reading: ETS-TOEFL阅读机经 - 4TZHNL54535MUJ64L$

According to paragraph 2, why would it have been difficult for humans to stay warm in Inner Eurasia before 200,000 years ago? A. Fire had not yet been discovered. B. Humans did not have access to skins or furs to help keep them warm. C. Humans had not yet learned how to bring fire into daily use. D. Lack of fuel made building fires on the steppes almost impossible.