Many people imagine that Alzheimer’’s disease (早老性痴呆病), the degenerative disorder that ultimately leaves sufferers with total memory loss, is an inevitable result of aging. This is not so. 【B1】 the risks of contracting the disease increase with age, there are many elderly people 【B2】 memories are perfect. Most of us are so ill- 【B3】 about all forms of memory loss that we label everything as "Alzheimer’’s". Alzheimer’’s disease itself can 【B4】 people as young as 30 and can progress either quickly or slowly. It can also 【B5】 the blame for other non-degenerative conditions such as deep depression. 【B6】 only an examination of the brain tissue during an autopsy (解剖) can produce an accurate 【B7】 of the disease. The causes of Alzheimer’’s are unknown. They may be either 【B8】 or environmental. A study in 1996 of 13,000 people whose parents or siblings had the disease showed they had five times 【B9】 chance of succumbing 【B10】 the age of 80 than those with no family 【B11】 of the problem. There are other factors, however. In a study of identical twins, it was found that only about half of the twin pairs developed Alzheimer’’s and , when both twins 【B12】 it, they did so as 【B13】 as 15 years apart. The possibility 【B14】 environment plays a part was 【B15】 by another 1996 study, this time of two groups of elderly Japanese men. One group lived in Hawaii, the other in Japan. The Hawaiian group had a much higher 【B16】 of the disease. Aluminum has been blamed for the development of Alzheimer’’s. This is because a high level of aluminum has been found in the brains of sufferers. The disease was first diagnosed at the beginning of the 20th century. It was at this time 【B17】 aluminum was becoming widely available for use in cooking pots. Memory loss, difficulty in 【B18】 familiar tasks, and problems with abstract thinking are all 【B19】 of the onset of the disease. One unusual feature is its impact on language. It attacks nouns first, 【B20】 verbs. Grammar is one of the last things to go.

A．description
B．illustration
C．demonstration
D．diagnosis