题目内容
（请给出正确答案）
设有两个级数
和
则下列结论中正确的是().
A.若
且(II)收敛,则(I)一定收敛
B.若
且(I)发散,则(II)一定发散
C.若
且(II)收敛,则(I)一定收敛
D.若
且(II)发散,则(I)一定发散
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更多“设有两个级数和则下列结论中正确的是().A.若且(II)收敛,则(I)一定收敛B.若且(I)发散,则(II)一”相关的问题
Researchers have established that when people are mentally engaged, biochemical changes occur in the brain that allow it to act more effectively in cognitive 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 Again. “Most of us don't need that kindof skill. Such specific training is of less interest than being able to maintain mental alertness.” Fozard and others say they challenge their brains with different mental skill, both because they enjoy them and because they are sure that their range of activities will help the way 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 health and size.”
6. People who are cognitively healthy are those _______.
A、who can remember large amounts of information
B、who are highly intelligent
C、whose minds are alert and receptive
D、who are good at recognizing different sounds
7. According to Fozards argument people can make their brains work more efficiently by _______.
A、constantly doing memory work
B、taking part in various mental activities
C、going through specific training
D、making frequent adjustments
8. The findings of James and other scientists in their work _________.
A、remain a theory to further proved
B、have been challenged by many other experts
C、have been generally accepted
D、are practiced by the researchers themselves
9. Older people are generally advised to ___________.
A、keep fit by going in for physical activities
B、keep mentally active by challenges through specific training
C、maintain mental alertness through specific training
D、maintain a balance between individual and group activities
10. What is the passage mainly about?
A、How biochemical changes occur in the human brain.
B、Why people should keep active not only physically but also mentally.
C、How intellectual activities influence brain-cell health
D、Why people should receive special mental training as they age.
在原点(0,0)处分别对每个自变量x或y(另一个看作常数)都连续,但是二元函数在原点(0,0)却不连续.
确定,则曲线y=y(x)在点(3,y(3))处的法线与0x轴交点的横坐标是().A.1/8In2+3
B.-1/8ln2+3
C.-8ln2+3
D.8ln2+3
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