【单选题】

The symptoms ofAlzheimer’s disease were long dismissed as normal consequences of human aging, but in the 1980’s the disease came to be recognized as the most common cause of intellectual deterioration in the elderly and middle-ageD、It is characterized by the death of nerve cells in the cerebral cortex--the part of the brain involved in complex function.

The major debilitating symptoms ofAlzheimer’s disease include serous forgetfulness -- particularly about recent events--and confusion.At first, the individual experiences only minor and almost imperceptible symptoms that are often attributed to emotional upsets or other physical illnesses. Gradually, however, the person becomes more forgetful, and this may be reported by anxious relatives. The person may neglect to turn off the oven, may misplace things, any recheck to see if a task was done, may take longer to complete a chore that was previously routine, or may repeat already-answered questions.As the disease progresses, memory loss and such changes in personality, mood, and behavior, such as confusion, irritability, restlessness and agitation, are likely to appear. Judgment, concentration, orientation, writing, reading, speech, motor behavior and naming of objects may also be affecteD、Even when a loving and caring family is available to give support, the victim ofAlzheimer’s disease is more likely to spend his or her last days in a nursing home or long-term care institution.At this time, there is no cure.
According to the passage, which of the following causesAlzheimer’s disease
A、Sever emotional stress.
B．Nutritional deficiency.
C．The death of nerve cells in the cerebral cortex.
D．Severe head traum