题目内容：

There is an English saying , “Laughter is the best medicine.” __1.__ Now, however, doctors have begun to look into laughter and the effects it has on the human body. They have found that laughter really can improve people’s health.

Tests were carried out to study the effects of laughter on the body. People watched the funny films while doctors checked their heart, blood pressure, breathing and muscles. __2.___ It increases blood pressure, the heart beating and breathing; it also works several groups of muscles in the face, the stomach, and even the feet. If laughter exercises the body, it must be beneficial.

___3.__ In one experiment, doctors produced pain in groups of students who listened to different radio programmes. The group that tolerated (忍受) the pain for the longest time was the groups which listened to a funny programmes.  ___4.___

In this way ___5.___ they help to improve their patients’ condition by encouraging them to laugh. They have found that even if their patients do not really feel like laughing, making them smile is enough to produce beneficial effects similar to those caused by laughter.

A.     The reason why laughter can reduce pain seems to be that it helps to produce a kind of chemicals in the brain which diminish (减少) both stress and pain.

B.      Until recently, few people took the saying seriously.

C.      Laughter and physical exercise have similar effects on the human body.

D.     It was found that laughter has similar effects to physical exercise.

E.      As a result of these discoveries, some doctors in the United States now hold laughter clinics.

F.      Laughter could produce a kind of chemical.

G.     Other tests have shown that laughter appears to be able to reduce the effect of pain on the body.