A、Because the number of the subjects was rather small. B、Because the significance of the survey was limited. C、Because the amoun

Caffeine and napping have something in common.
    They both make you feel alert and can enhance your performance, whether that’s driving, working or studying.
    But some people are convinced that drinking a cup of coffee before taking a nap gives you extra energy when you wake up.
    Drinking coffee can also help us get through the day. And since the 1990s, researchers have been studying how combining the two might help.
    In a 1997 study, 12 sleep-deprived people drank the equivalent of one large cup of brewed coffee and five minutes later had the chance to nap for 15 minutes. They then did some driving tests in a simulator to check their alertness.
    Although drinking a coffee (without a nap) helped their driving performance, combining caffeine with a nap—a coffee nap—improved it even further.
    People who took a coffee nap were less likely to drift out of their lanes on a two-hour monotonous simulated drive.
    This was compared to when they just drank a cup of coffee (and had no nap) or when they had a cup of decaffeinated coffee (and without a nap).
    A coffee nap even helped performance if people dozed during their nap time rather than falling into a deeper sleep. A coffee nap also reduced sleepiness once people got up, with people remaining alert for a couple of hours.
    However, this early, small study was questioned. For instance, we don’t know how much coffee the people in the study were used to drinking or if they were what researchers call caffeine-naive and so more likely to experience a greater caffeine "hit. "
    Questions 9 to 11 are based on the passage you have just heard.
    9. What did the 1997 study find about people who took a coffee nap?
    10. What did the study find about the benefit of a coffee nap?
    11. Why was the study questioned according to the speaker?