19. Over 20 studies have shown a person's goes up when they are sleep deprived.
20. Insufficient sleep is one of three factors which explain the .
21. People who are given the by doctors find it more effective if they sleep properly.
22. Walker has described how a lack of deep sleep is linked to in young children.
Which TWO of these things are recommended by Matthew Walker?
Which TWO of the following statements are true of Matthew Walker?