根据下列文章,请回答 23～30 题。 Exercising Your Memory 1 Aging does not mean a dramatic decline in memory power, unless you help it happen by letting your mind go． 2 That’s not to say that memory doesn’t change throughout life．Researchers divide memory into categories based on the Length of time when memories are stored．One system divides it up as short—term(1ess than one minute；Remembering a telephone number while you dial，for instance)，long-term(over a period of years)and very long-term memory(over a lifetime)． 3 Short．term memory isn’t mastered until about age 7．but after that you never lose it．Long-term memory, however，involves more effort and skill and changes more through life．It's not until the early teens(十几岁)that most people develop a mature long—term memory． 4 First，we must get information into our heads through learning．Learning strategies can get rusty(生锈的)without constant use．High school and college students，who are forced to repeatedly exercise their long-term memory abilities(at least long—term enough to get them through a final exam)，usually do well on memory tests．The longer you stay in school。the more chance you get to polish your learning skills．It's no wonder that more highly educated people have more effective memory skills throughout life． 5 Although older people in general learn somewhat more slowly than they did when younger, a dramatic difference exists between those who stay intellectually active reading，discussing，taking classes，thinking——and those who do not．Giving the brain a daily workout(锻炼)is just as important as exercising your muscles．Brainwork keeps your learning strategies in shape，and this helps your memory to function at full capacity． 6 The next part of a healthy long—term memory is retention(记忆力)，the ability to store what you have learned．Memory researchers still do not know whether memories are lost——whether they still exist in the brain but our mental searching cannot turn them up，or have disappeared entirely as our brain ages． 7 The third necessity for memory is recall。the ability to bring to mind the memories we have stored．Again。while aging has widely different effects on the recall abilities of different people。research indicates that the older we get，the longer it takes to recall facts．But slower recall is still recall．In fact．aging does not seem to have any effect on forgetting at all．which takes place at the same rate in younger and older people． 第 23 题 Paragraph 3__________