Questions 21 to 25 are based on the following passage:
21. People who are cognitively healthy are those _________.
A) whose minds are alert and receptive
B) who are highly intelligent. C) who can remember large amounts of information
D) who are good at recognizing different sounds
22. According to Fozard's argument, people can make their brains work more efficiently by _________.
A) constantly doing memory work
B) making frequent adjustments
C) going through specific training
D) taking part in various mental activities
23. The findings of James and other scientists in their work _________.
A) remain a theory to be further proved
B) have been challenged by many other experts
C) are practised by the researchers themselves
D) have been generally accepted
24. Older people are generally advised to _________.
A) keep mentally active by challenging their brains
B) keep fit by going in for physical activities
C) maintain mental alertness through specific training
D) maintain a balance between individual and group activities
25. What is the passage mainly about?
A) How biochemical changes occur in the human brain.
B) Why people should receive special mental training as they age.
C) How intellectual activities influence brain-cell health.
D) Why people should keep active not only physically but also mentally.
Researchers have established that when people are mentally engaged, biochemical changes occur in the brain that allow it to act more effectively in cognitive (认知的) areas such as attention and memory. This is true regardless of age.
注：1."it"指代"brain" 2.mentally engaged 动脑筋，思考问题
3.第一句是主题句
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