Read the following passage and choose the most likely answer to each of the following questions.
Researchers have established that when people are mentally engaged (投入的), biochemical (生物化学的) changes occur in the brain that allow it to act more effectively in cognitively (认知的) areas such as attention and memory. This is true regardless of age. People will be alert and receptive if they are faced with information that gets them to think about things they are interested in. And someone with a history of doing more rather than less will go into old age more cognitively sound than someone who has not had an active mind.
Many experts are so convinced of the benefits of challenging the brain that they are putting the theory to work in their own lives. "The idea is not necessarily to learn to memorize enormous amounts of information," says James Fozard, associate director of the National Institute on Aging. "Most of us don't need that kind of skill. Such specific training is of less interest than being able to maintain mental alertness. " Fozard and others say they challenge their brains work.
Gene Cohen, acting director of the same institute, suggests that people in their old age should engage in mental and physical activities individually as well as in groups. Cohen says that we are frequently advised to keep physically active as we age, but older people need to keep mentally active as well. Those who do are more likely to maintain their intellectual abilities and to be generally happier and better adjusted. "The point is, you need to do both." Cohen says, "Intellectual activity actually influences brain-cell's health and size."
Older people are generally advised to （ ）.
A、
keep fit by going in for physical activities
B、
keep mentally active by challenging their brains
C、
maintain mental alertness through specific training
D、
maintain a balance between individual and group activities
【正确答案】：D
【题目解析】：
原文第三段的第一句讲到：Gene Cohen，同一研究所的代理主任，建议老年人应该单独地和集体地进行心理和身体活动。故D项正确。