A、Timing and length. B、Necessity and variability. C、Necessity and flexibility. D、Timing and variability. B原文中明确提到，关于睡眠科学的两个基本发现是

Researchers have found significant variations in the length, timing, and quality of people’s sleep. For instance, children and adolescents need much more sleep than do adults. Women tend to have more insomnia than men. Some people do well with 6 hours of sleep a night, others need at least 8 or 9. Some people are most alert early in the morning, while others are slow to awaken and only feel truly conscious late at night. All of this is to say, there is no right or normal way of sleeping. There is only what makes you and your body feel rested.
    These two basic findings of sleep science—the necessity and variability of sleep—have important implications for how work and school activities are scheduled. For example, it’s not healthy for schools or businesses to establish a single schedule governing the activities of a large group of people without building in flexibility for the significant number of people whose bodily rhythms will need a somewhat different schedule to stay optimally functional.
    It often takes time for scientific research to overcome entrenched cultural attitudes. A view of sleep as nothing but wasted time has prevailed among many people. Denying the need for sleep has become a symbol of heroic devotion to productivity, innovation, and success. Anyone who believes otherwise is simply weak or lazy, a slacker with no drive.
    That attitude should be left behind. The truth is that, given the enormous challenges facing society today, people with sound sleep patterns are more creative, better able to respond adaptively to unusual or unexpected circumstances as compared to sleep-deprived people.
    Questions 12 to 15 are based on the passage you have just heard.
    12. What have researchers found about sleep?
    13. What does the finding about sleep suggest?
    14. What are the two basic findings of sleep science?
    15. What is people’s rooted attitudes towards sleep?