is a problem with certain nerve cells in the brain. Normally, these nerve cells make an important chemical called dopamine (多巴胺). Dopamine sends signals to the part of your brain that controls movements. It lets your muscles move smoothly and do what you want them to do. When you have Parkinson's, these nerve cells break down. Then you no longer have enough dopamine, and you have trouble moving the way you want to.

　　2 No one knows for sure what makes these nerve cells break down. But scientists are doing a lot of research to look for the answer. They are studying many possible causes, including aging and poisons in the environment. Abnormal genes seem to lead to Parkinson's disease in some people. But so far, there is not enough proof to show that it is always inherited.

　　3 Tremor (颤抖) may be the first symptom you notice. It is one of the most common signs of the disease, although not everyone has it. Tremor often starts in just one arm or leg or only on one side of the body. It may be worse when you are awake but not moving the affected arm or leg. It may get better when you move the limb or you are asleep. In time, Parkinson's affects muscles all through your body, so it can lead to problems like trouble swallowing or constipation (便秘). In the laterstages of the disease, a person with Parkinson's may have a fixed or lank expression, trouble speaking, and other problems. Some people have a decrease in mental skills.

　　4 At this time, there is no cure for Parkinson's disease. But there are several types of medicines that can control the symptoms and make the disease easier to live with. You may need to take several medicines to get the best results.

　　23. Paragraph 1 __________.

　　24. Paragraph 2 __________.

　　25. Paragraph 3 __________.

　　26. Paragraph 4 __________.

　　A. Means of Diagnosis of the Disease

　　B. Tips for Patients with the Disease

　　C. Common Treatment for the Disease

　　D. Definition of Parkinson's D