根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。
There is an English saying: “  .” Until recently, few people took the saying seriously. Now, however, doctors have begun to look into laughter and the effects it has on the human body.    
Tests were carried out to study the effects of laughter on the body. People watched funny films while doctors checked their hearts, blood pressure, breathing and muscles. It was found that laughter has similar effects to physical exercise.    . If laughter exercises the body, it must be beneficial.
Other tests have shown that laughter appears to be able to reduce the effect of pain on the body. In one experiment doctors produced pain in groups of students who listened to different radio programs. The group that tolerated(忍耐) the pain for the longest time was the group which listened to a funny program.  
____. 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．Laughter can prolong one’s life.

B．As a result of these discoveries, some doctors in the United States now hold laughter clinics in which they help to improve their patients’ condition by encouraging them to laugh.

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

D．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.
E. Although laughter helps cure the disease, doctors still can not put this theory into clinic practice.
F. Laughter is the best medicine.
G. They have found that laughter really can improve people’s health.