1.Many of us believe that a person‘s mind becomes less active as he grows older. But this is not true， according to Dr Jarvik， professor of psychiatry at the University of California. She has studied the mental functioning of aging persons for several years. For example， one of her studies concerns 136 pairs of identical twins， who were first examined when they were already 60 years old. As Dr Jarvik continued the study of the twins into their 70s and 80s， their minds did not generally decline as was expected.
   However， there was some decline in their psycho-motor speed. This means that it took them longer to accomplish mental tasks than it used to. But when speed was not a factor， they lost very little intellectual ability over the years. In general， Dr Jarvik‘s studies have shown that there is no decline in knowledge or reasoning ability. This is true not only with those in their 30s and 40s， but with those in their 60s and 70s as well.
    It is true that older people themselves often complain that their memory is not as good as it once was. However， much of what we call “loss of memory” is not that at all. There usually was incomplete learning in the first place. For example， the older person perhaps had trouble hearing， or poor vision， or inattention， or was trying to learn the new thing at too fast a pace. In the cases where the older person‘s mind really seems to decay，it is not necessarily a sign of decay due to old age. Often it is simply a sign of a depressed emotional state.(10分)


1.1  This passage is mainly about ____.(2分)
A. how Dr Jarvik studied mental functioning of the twins.
B. what caused mental decay.
C. the results evidenced by Dr Jarvik‘s studies.
D. the difference between middle – aged and older persons