填空题

Cats are creatures of habit. They like go to sleep about the same time every day and for a certain (S1) ______ of time. They seem to have a (S2) ______ clock inside them that tells them when to sleep. Cats supplement their regular sleep with (S3) ______ cat naps. Some experts feel that humans could also (S4) ______ from this habit. Cat naps help to build up energy in the body. They are also a good way to overcome (S5) ______ . Since cats have moods similar to those of humans, some experts believe that people can improve their moods and (S6) ______ by cat napping. People might become happier and more (S7) _______________. (S8) _____________________________ The naps would usually last from 15 to 30 minutes. Winston Churchill took cat naps. So did President Harry Truman, John F. Kennedy, and Lyndon B. Johnson. (S9) ________________________ Napping was their secret. (S10) ___________________________________. S10