TOEFL Listening: ETS-TOEFL听力机经 - 7349U2UPIE0B9BDRP$

According to the professor, what do biological-clock theories propose? A. That an organism's behavior plays an important role in the aging process B. That the aging process is genetically predetermined C. That organisms age as the result of a gradual loss of energy D. That environmental conditions can speed or slow the aging process