Researchers have established that when people are mentally ____1____, biochemical changes occur in the brain that allow it to ____2____ more effectively in cognitive (认知的) areas such as attention and memory. This is true ____3____ age. 

People will be alert and ____4____ if they are faced with information that ____5____ them to think about things they are ____6____ in. And someone with a history of doing more ____7____ less will go into old age more cognitively sound than someone who has not had an active ____8____. 

Many experts are so convinced ____9____ the benefits of challenging the brain that they are ____10____ the theory to work in their own lives. “The idea is not ____11____ to learn to memorize enormous ____12____ of information,” says James Fozard, associate director of the National Institute on Aging. “Most of us don’t need that kind of skill. Such specifi c training is____13____ less interest than being able to maintain mental ____14____.” Fozard and others say they challenge their brains with different mental skills, ____15____ because they enjoy them and because they are sure that their range of activities will help the ____16____ their brains work. 

Gene Cohen, acting director of the same institute, says that we are frequently advised to keep ____17____ active as we age, but older people need to keep mentally active as well. Those who ____18____ are more ____19____ to maintain their intellectual abilities and to be generally happier and better adjusted. And intellectual activity actually ____20____ brain-cell health and size. 

1. A. strengthened B. alert  C. engaged  D. activated 

2.A. act  B. think  C. learn  D. respond 

3.A. as to B. regardless of  C. in spite of  D. despite 

4.A. deceptive  B. inceptive  C. perceptive  D. receptive 

5.A. makes B. lets  C. pushes  D. gets 

6.A. familiar  B. interested  C. Impressed  D. attracted 

7.A. rather than  B. other than  C. instead of  D. in place of 

8.A. brain  B. mind  C. intellect  D. mentality 

9.A. with  B. at  C. of  D. in 

10. A. putting  B. trying C. using  D. laying 

11. A. certainly  B. necessarily C. immediately D. quickly 

12. A. number B. numbers C. amount  D. amounts 

13. A. of  B. in  C. with  D. at 

14. A. function B. alertness  C. activity  D. shape 

15. A. both  B. not C. and  D. which 

16. A. style  B. effect C. efficiency  D. way  

17. A. bodily  B. physically C. spiritually  D. intellectually 

18. A. do  B. act  C. work  D. laugh 

19. A. possible B. able C. likely  D. often 

20. A. affects  B. influences  C. reflects  D. changes