单项选择题

For three decades we’’ve heard endlessly about the virtues of aerobic (increasing oxygen consumption) exercise. Medical authorities have praised running and jumping as the key to good health, and millions of Americans have taken to the treadmill(踏车) to reap the rewards. But the story is changing. Everyone from the American Heart Association to the surgeon general’’s office has recently embraced strength training as a complement to aerobics. And as weight lifting has gone mainstream, so has the once obscure practice known as "Super Slow" training. Enthusiasts claim that by pumping iron at a snail’’s pace-making each "rep"(repeat) last 14 seconds instead of the usual seven-you can safely place extraordinary demands on your muscles, and call forth an extraordinary response. Slow lifting may not be the only exercise you need, as some advocates believe, but the benefits are often dramatic.   Almost anyone can handle this routine. The only requirements are complete focus and a tolerance for deep muscular burn. Fox each exercise-leg press, bench press, shoulder press and so on-you set the machine to provide only moderate resistance. But as you draw out each rep, depriving yourself of impetus, the weight soon feels unbearable. Defying the impulse to stop, you keep going until you can’’t complete a rep. Then you sustain your vain effort for 10 more seconds while the weight sinks gradually toward its cradle. Intense Uncomfortable Totally. But once you embrace muscle failure as the goal of the workout, it can become almost pleasure.   The goal is not to burn calories while you’’re exercising but to make your body burn them all the time. Running a few miles many make you sweat, but it expends only 100 calories per mile, and it doesn’’t stimulate much bone or muscle development. Strength training doesn’’t burn many calories, either. But when you push a muscle to failure, you set off a pour of physiological changes. As the muscle recovers over several days, it will thicken-and the new muscle tissue will demand sustenance. By the time you add three pounds of muscle, your body requires an extra 9,000 calories a month just to break even. Hold your diet steady and, very quickly, you are vaporizing body fat.   One might have benefited from any strength-training program. But advocates insist the slow technique is safer and more effective than traditional methods. According to the author," Super Slow" training

A.has been misunderstood for decades.
B.has been widely accepted recently
C. has been the basis of weight lifting.
D.has become the nucleus of aerobics.
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Solar energy is called a renewable resource because on a human time scale it is essentially inexhaustible, it is expected to last at least 6.5 billion years while the sun completes its life cycle. 46) A potentially renewable resource can be renewed fairly rapidly (hours to several decades) through natural processes, examples of which include forest trees, grassland grasses, wild animals, fresh lake and stream water, groundwater, fresh air, and fertile soil.47) One important potentially renewable resource for us and other species is biological diversity or biodiversity, which consists of the life forms that can best survive variety of conditions currently found on Earth. Kinds of biodiversity include (1) genetic diversity( variety in the genetic makeup among individuals within a single species), (2) species diversity (variety among the species or unique forms of life found in different habitats of the planet), and ( 3 ) ecological diversity (variety of forests, deserts, grasslands, streams, lakes, oceans, wetlands, and other biological communities). 48)This rich variety of genes, species, and biological communities gives us food, wood, fibers, energy, raw materials, industrial chemicals, and medicines―all of which pour hundreds of billions of dollars into the world economy each year. Earth’’s vast list ’’of life forms and biological communities also provides free recycling and purification services and natural pest control.Potentially renewable resources, however, can be exhausted. 49)The highest rate at which a potentially renewable resource can be used indefinitely without reducing its available supply is called its sustainable yield. If a resource’’s natural replacement rate is exceeded, the available supply begins to shrink―a process known as environmental degradation.Several types of environmental degradation can change potentially renewable resources into nonrenewable or unusable resources. In the United States, one-fourth of the groundwater withdrawn each year is not replenished (filled up again). Between 25% and 50% of the world’’s wetlands (55% in the U. S. ) have been drained, built upon, or seriously polluted. Almost half of the world’’s tropical forests have been cleared. Thousands of wildlife species become extinct each year, mostly because of human activities. If habitat destruction continues at present rates, as many as 1.5 million species could disappear over the next 25 years―a drastic loss in vital Earth capital. 50)These examples help explain why most environmental scientists believe that over the next few decades, the danger of degradation and exhaustion is greatest for potentially renewable resources, not nonrenewable resources ( except for petroleum and perhaps a few scarce minerals for which we can’’t find economically and environmentally acceptable substitutes).