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Walking, if you do it vigorously enough, is the overall best exercise for regular physical activity. It requires no equipment, everyone knows how to do it and it carries the (1) risk of injury. The human body is designed to walk. You can walk in parks or along a river or in your neighborhood. To get (2) benefit from walking, aim for 45 minutes a day, an average of five days a week.Strength training is another important (3) of physical activity. Its purpose is to build and (4) bone and muscle mass, both of which shrink with age. In general, you will want to do strength training two or three days a week, (5) recovery days between sessions.Finally, flexibility and balance training are (6) important as the body ages. Aches and pains are high on the list of complaints in old age. The result of constant muscle tension and stiffness of joints, many of them are (7) , and simple flexibility training can (8) these by making muscles stronger and keeping joints lubricated (润滑). Some of this you do whenever you stretch. If you watch dogs and cats, you’ll get an idea of how natural it is. The general (9) is simple: whenever the body has been in one position for a while, it is good to (10) stretch it in an opposite position.A．allowingB．avoidableC．brieflyD．componentE．determinedF．helpingG．increasinglyH．lowestI．maintainJ．maximumK．preventL．principleM．provokeN．seriouslyO．topic （9）处应填（）

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So many people use the cell phones so frequently every day. But (1) little is certain about the health effects of its use. Manufacturers (2) that cell phones meet government standards for safe radio-frequency radiation emission, but enough studies are beginning to document a possible (3) in rare brain tumors (肿瘤), headaches and behavioral disorders in children to cause concern. So far, the evidence isn’t (4) on whether the use of cell phones (5) to any increased risk of cancer. In a new trial, researchers asked 47 volunteers to (6) in a project to measure glucose (葡萄糖) consumption in the brain by scanning the brain to see how cells use energy. For both 50-minute scans, the volunteers had a cell phone (7) to each ear. During the first scan, the devices were turned off, but for the second scan, the phone on the right ear was (8) on and received a recorded-message call, although the volume was muted (消音) so the noise wouldn’t bias the results. The results of the second scan showed that the (9) of the brain nearest to the device had higher rates of glucose consumption than the rest of the brain. The study shows that cell phones can change brain activity, and (10) a whole new avenue for scientific inquiry, though it doesn’t say anything about whether cell-phone radiation can cause cancer.A．conclusiveB．contributesC．deriveD．expressesE．fixedF．immenselyG．increaseH．maintainI．missionJ．participateK．particularL．providesM．regionsN．surprisinglyO．switched （8）处应填（）

With the world’s population estimated to grow from six to nine billion by 2050, researchers, businesses and governments are already dealing with the impact this increase will have on everything from food and water to infrastructure (基础设施) and jobs. Underlying all this (1) will be the demand for energy, which is expected to double over the next 40 years.Finding the resources to meet this demand in a (2) sustainable way is the cornerstone (基石) of our nation’s energy security, and will be one of the major (3) of the 21st century. Alternative forms of energy—bio-fuels, wind and solar, to name a few—are 4 being funded and developed, and will play a growing (5) in the world’s energy supply. But experts say that, even when (6) , alternative energy sources will likely meet only about 30% of the world’s energy needs by 2050.For example, even with (7) investments, such as the ＄93 million for wind energy development (8) in the American Recovery and Reinvestment Act, important alternative energy sources such as wind and bio-fuels (9) only about 1% of the market today.Energy and sustainability experts say the answer to our future energy needs will likely come from a lot of (10) —both traditional and alternative.A．stableB．solutionsC．significantD．roleE．progressF．marvelousG．includedH．growthI．exactlyJ．consistK．compriseL．competitionsM．combinedN．challengesO．certainly （7）处应填（）

So many people use the cell phones so frequently every day. But (1) little is certain about the health effects of its use. Manufacturers (2) that cell phones meet government standards for safe radio-frequency radiation emission, but enough studies are beginning to document a possible (3) in rare brain tumors (肿瘤), headaches and behavioral disorders in children to cause concern. So far, the evidence isn’t (4) on whether the use of cell phones (5) to any increased risk of cancer. In a new trial, researchers asked 47 volunteers to (6) in a project to measure glucose (葡萄糖) consumption in the brain by scanning the brain to see how cells use energy. For both 50-minute scans, the volunteers had a cell phone (7) to each ear. During the first scan, the devices were turned off, but for the second scan, the phone on the right ear was (8) on and received a recorded-message call, although the volume was muted (消音) so the noise wouldn’t bias the results. The results of the second scan showed that the (9) of the brain nearest to the device had higher rates of glucose consumption than the rest of the brain. The study shows that cell phones can change brain activity, and (10) a whole new avenue for scientific inquiry, though it doesn’t say anything about whether cell-phone radiation can cause cancer.A．conclusiveB．contributesC．deriveD．expressesE．fixedF．immenselyG．increaseH．maintainI．missionJ．participateK．particularL．providesM．regionsN．surprisinglyO．switched （7）处应填（）

Walking, if you do it vigorously enough, is the overall best exercise for regular physical activity. It requires no equipment, everyone knows how to do it and it carries the (1) risk of injury. The human body is designed to walk. You can walk in parks or along a river or in your neighborhood. To get (2) benefit from walking, aim for 45 minutes a day, an average of five days a week.Strength training is another important (3) of physical activity. Its purpose is to build and (4) bone and muscle mass, both of which shrink with age. In general, you will want to do strength training two or three days a week, (5) recovery days between sessions.Finally, flexibility and balance training are (6) important as the body ages. Aches and pains are high on the list of complaints in old age. The result of constant muscle tension and stiffness of joints, many of them are (7) , and simple flexibility training can (8) these by making muscles stronger and keeping joints lubricated (润滑). Some of this you do whenever you stretch. If you watch dogs and cats, you’ll get an idea of how natural it is. The general (9) is simple: whenever the body has been in one position for a while, it is good to (10) stretch it in an opposite position.A．allowingB．avoidableC．brieflyD．componentE．determinedF．helpingG．increasinglyH．lowestI．maintainJ．maximumK．preventL．principleM．provokeN．seriouslyO．topic （6）处应填（）