A、Laughing is a learned behavior. B、Laughing is a good medicine to patients. C、Laughing is easier than battling with an illness.

W: We’ve all heard the saying "Laughter is the best medicine." How important is it to our health, Dr. Berk?
M: This saying has been scientifically proven! A year-long study of heart attack victims done at the Oakhurst Health Research Institute in California found that of those patients who spent half an hour a day watching comedy videos, 10 percent had a second heart attack, whereas 30 percent of those who did not watch had a second attack.
W: Wow! Laughter is really a good medicine to patients. Can you give us another example?
M: Sure! Norman Cousins, editor of the Saturday Review, learned this during a battle with an illness. He discovered that his condition improved when he enjoyed himself and watched funny movies.
W: You said Norman learned this? Do we have to learn to laugh?
M: Not necessarily. Since laughing is something people can do sitting down, costs no money, and requires no special exercise equipment or skill, it’s the perfect workout for anyone who doesn’t have the time or desire to participate in a regular fitness program.
W: Oh. Do you have such a program to offer to the general public?
M: Yes, we do. It’s called the Smile Time-Out You take a deep breath, smile, exhale, and say "Aaah" while visualizing all your muscles and cells smiling. Then add to that a memory of a time you felt really good and laughed and laughed.
W: What about the situation in which you aren’t in a mood to laugh?
M: Even when you fake a smile or laugh, you get the same physiological benefits as when it’s the real thing, because your mind is smart, but your body is stupid and can’t tell the difference!
19. What did the year-long study of heart attack victims find?
20. What is Norman’s example meant to prove?
21. What is the so-called Smile Time-Out?
22. What can we learn about smile or laugh according to Dr. Berk?