Passage 5 Any brain exercise is better than being a total mental couch potato. But the activities with the most _1_ are those that require you to work beyond what is easy and comfortable. Playing _2_ rounds of games and watching the latest documentary marathon on the History Channel may not be enough. Just as your muscles grow stronger with use, mental exercise keeps your mental skills and memory in tone. But what kind of exercise is best for the brain? Here are some suggestions. Be a lifelong learner. Continuing to learn new things can build and _3_ the connections between brain cells. _4_ your brain. Think of all mental activities as a continuous whole. Watching a TV documentary would be on the passive, mildly challenging end of the _5_, while learning how to converse in a new language would be on the active, very challenging end. When it comes to cognitive reserve, _6_ challenging tasks have the biggest impact. Get uncomfortable. One stereotype of aging is that young people are bold explorers but older I people are _7_ homebodies who “know what they like.” Getting out of your comfort zone from time to time challenges your mental skills. An example of this would be traveling to a city that you haven’t been to before, which forces you to _8_ unfamiliar surroundings. Be social. Social _9_,aging researchers have discovered, puts people at risk of losing some of the brain reserves they have built up over a lifetime. There are many ways to be social. One good way is working as a volunteer in a social setting, which allows you to have contact with _10_ types of people and puts you in new situations. A) endless B) isolation C) maintain D) spectrum E) evidently F) navigate G) timid H) frantic I) mentally J) diverse K) impact L) deprive M) alternative N) excursion O) strain 第1空答案是：