A、4. B、5. C、6. D、7. C文中提到“教授区分了6种睡觉姿势……”，故选C。

Whether it’s curled up, flat on the stomach or stretched out across the bed, the way people sleep reveals their personality, a British sleep expert said. Professor Chris Idzikowski, director of the Sleep Assessment and Advisory Service, has identified six common sleep positions and what they mean. Crouched in the fetal position is the most popular sleep pattern and favored by 51 percent of women, according to the results of the study he conducted for a large hotel group. Fetal sleepers tend to be shy and sensitive while people who take the soldier position, flat on their back with arms at their sides, are quiet and reserved. Sleeping on one’s side with legs outstretched and arms down in what Idzikowski refers to as the log, indicates a social, easy-going personality. But if the arms are out-stretched in a yearning position, the person tends to be more suspicious. The freefall, flat on the stomach with the hands at the sides of the head, is the most unusual position. Only 6.5 percent of people prefer it and they are usually rash and sociable. Unassuming, good listeners usually adopt the starfish position—on the back with outstretched arms and legs. Idzikowski, who identified the positions by comparing personality traits of people, their preferred way of sleeping and the most common positions, said once a sleeping style is adopted it is rarely changed.
19. How many common sleep positions did the professor identify?
20. What is true about sleepers in the soldier position?
21. What is not revealed by the study?