Alzheimer's disease is a major national health problem. Nearly 2 million Americans over the age of 65 have Alzheimer's disease. It is a leading cause of death among the elderly. But Alzheimer's disease is not confined   to the aged. There may be a million or more people under the age of 65 suffering from the disease. At one time, people suffering from the disease were said to be "getting old". The disease was thought to be a natural part of growing old, but it is now known that Alzheimer's disease strikes young and old alike. It is an organic   disease that destroys brain cells. Alzheimer's disease affects the patient's memory, speech, and movement. In the beginning stages of the disease, the patient may seem slightly confused. He may have trouble speaking, then the patient's memory begins to fail. He may forget dates, numbers, names and plans. As the disease progresses, the patient may not recognize family and friends. These symptoms  often cause terrible anxiety in the patient. He may feel lost and frightened. Sometimes the patient reacts with wild and bad behavior. In the last stages of the disease, the patient may not be able to take care of himself. He may have lost the ability to speak and walk. Scientists don't know exactly what causes Alzheimer's disease. It may be caused by a virus  .It may be caused by a poisonous substance  in the environment. At present, there is no cure for the disease. But there are ways to slow its progress. Exercise and physical treatment can help the patients of this disease. The press of Alzheimer's disease can be slowed by  _  .
operation a change in environment medicines physical treatment and exercise