根据下列材料，请回答下列各题 The following is a passage about laughter. After reading it, you are required to complete the outline below it ( No. 46 to No. 50 ). You should write your answers briefly ( in no more than three words) on the Answer Sheet correspondingly. There is an old saying in English: 'Laughter is the best medicine'. Until recently, few people took the say- ing very seriously. Now, however, doctors have begun to investigate laughter and the effects it has on the human body. They have found evidence that laughter really can improve people' s health. Tests were carried out to study the effects of laughter on the body. People watched funny films, while doc- tors checked their heart rate, blood pressure, breathing and muscles. It was found that laughter has similar effects to physical exercise. It increases blood pressure, the heart rate and the rate of 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. Other tests have shown that laughter appears to be capable of reducing the effect of pain on the body. There is also some evidence to suggest that laughter helps the body' s immune system, that is, the system which fights infection. As a result of these discoveries, some doctors and psychiatrists (精神病学家)in the United States now hold laughter clinics, in which they try to improve their patients' condition by encouraging them to laugh. Laughter really can 46______________