During sleep, the fatigue (疲劳) of the body (47) and recuperation (恢复) begins. The tired mind gathers new energy. Once awake, the memory improves, and annoyance and problems are seen in a better (48) .
Some s require little sleep; others need eight to ten hours in every twenty-four. (49) sleep six to eigh hours daily and, as they grow older, the (50) gradually diminishes. Young students may need twelve hours; university students may need ten. A worker with a (51) demanding job may also need ten, whereas an executive worker under great pressure may manage on six to eight. Many famous people are reputed to have required little sleep. Napoleon, Thomas Edison and Charles Darwin apparently (52) only four to six hours a night.
Whatever your (53) need, you can be sure that by the age of thirty you will have slept for a total of more than twelve years. By that age you will also have developed a sleep (54) : a favorite hour, a favorite bed, a favorite position, and a formula you need to follow in order to rest comfortably.
Investigators have tried to find out how long a person can go without sleep. Several people have reached more than 115 hours, nearly five days, (55) animals kept awake for from five to eight days have died of exhaustion. The (56) for human beings is probably about a week.

• [A] disappears[I] averaged
• [B] amount[J] data
• [C] perspective [K] whereas
• [D] Infants [L] People
• [E] routine [M] doubtful
• [F] limit [N] entertain
• [G] physically [O] instinct
• [H] individual