单项选择题

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 health.
D．Why people should keep active not only physically but also mentally.

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单项选择题

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 practiced by the researchers themselves
D．have been generally accepted

单项选择题

In order to enter the Marathon, participants must______.

A．pay an entrance fee
B．assemble in one specific area
C．be able to run 26 miles, 385 yards
D．compete for the right to take part