Please answer the following question: Read the following article and select the best answer. Article: Many of us believe that a person's mind becomes less active as he grows older.But this is not true,according to Dr.Lissy F.Jarvik,professor of psychiatry at the University of California,Los Angeles,and a board member of the New Center for Aging at the Veterans Hospital.She has studied the mental functioning of aging persons for several years.For example,one of her studies concerns 136 pairs of 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 into the 30s and 40s,but into the 60s and 70s as well. As for learning new things,and ability to remember,studies by Dr.Jarvik and others show that the old are equal to the young.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 a11. In the cases where the older person's mind really seems to decline,it is not necessarilv a sign of a decay due to becoming old or"senility".Often it is simply a sign of a depressed emotional state.This depression usually can be got rid of by counseling with a psychologist,or medicine which fights depression. In American society,when an older person loses something,we tend to call him or her"senile".But notice that when a younger person loses something,he does not blame it on senility or loss of memory.He finds some other excuse! Question: Both younger and older persons should realize that_. - a sign of a decay due to old age or"senility''is a common thing - older persons are wiser than younger ones because of different knowledge amount - senility or mental decay due to aging is much less common than most of us believe - a sign of a depressed emotional state is not a reason of decay
A:
senility or mental decay due to aging is much less common than most of us believe