阅读下面的短文。每篇短文的后面有五个问题，每个问题有四个备选答案。请根据短文的内容选择最佳答案。每个试题计3分,共计15分
　　Why Humans Walk on Two Legs
　　A team of scientists that studied chimpanzees trained to use treadmills has gathered new evidence suggesting that our earliest apelike ancestors started walking on two legs because it required less energy than getting around on all fours．
　　“When our earliest ancestors started walking on two legs，they took the first steps toward becoming human,” said lead researcher Michael Sockol of UC Davis1．“Our findings help an,swer why．” Sockol worked for two years to find an animal trainer willing to coax adult chimps to walk on two legs and to “knucklewalk” on all fours on the sort of treadmill found in most gyms．
　　The five chimps also wore face masks used to help the researchers measure oxygen consumption．While the chimps worked out，the scientists collected metabolic and other data that allowed them to calculate which method of locomotion used less energy and why．The team gathered the same information for four adult humans walking on a treadmill．
　　Tile researchers found that human walking used about 75 percent less energy and burned 75 percent fewer calories than quadrupedal and bipedal2 walking in chimpanzees． They also found that for some but not all of the chimps，walking on two legs was no more costly than knucklewalking．
　　“We were prepared to find that all of the chimps used more energy walking on two legs but that finding wouldn’t have been as interesting,” Sockol said．“What we found was much more telling． For three chimps，bipedalism3 was more expensive，but for the other two chimps，this wasn’t the case．One spent about the same energy walking on two legs as on four．The other used less energy walking upright．” These two chimps had different gaits and anatomy than their knucklewalking peers．
　　Taken together，the findings provide support for the hypothesis that anatomical differences affecting gait existed among our earliest apelike ancestors，and that these differences provided the genetic variation which natural selection could act on when changes in the environment gave bipeds an advantage over quadrupeds．
　　Fossil and molecular evidence suggests the earliest ancestors of the human family lived in forested areas in equatorial Africa in the late Miocene era some 8 to 10 million years ago，when changes in climate may have increased in distance between food patches．That would have forced our earliest ancestors to travel longer distances on the ground and favored those who could cover more ground using less energy．
　　“This isn't the complete answer,” Soekol said．“But it’s a good piece of a puzzle humans have always wondered about；How and why did we become human? And why do we alone walk on two legs?”
　　词汇：
　　chimpanzee/5tFimpEn5zi:/n．黑猩猩 (又作 chimp )
　　biped/5baiped/n．二足动物
　　gait/^eit/n．步态，步法
　　anatomic/7AnE5tCmik/adj．解剖 (学)的
　　quadruped/5kwCdrJped/n．四足动物的
　　Miocene/5maiEsi:n/n．＆．adj．中新世 (的)
　　Calorie/5kAlEri/n．卡 (路里) ,小卡
　　treadmill/5tredmIl/n．踏轮；踏车；单调工作
　　coax/kEuks/v．哄，哄劝
　　knucklewalk v．用膝关节走路
　　metabolic/7metE5bClik/adj．(新陈) 代谢的
　　locomotion/lEJkE5mEJF(E)n/n．运动 (力)
　　注释：
　　1． UC Davis：加州大学戴维斯分校。UC是University of California(加利福尼亚大学)的缩写，该校有多个分校，UC Davis是其中一个。Davis以前是UC Berkeley分校的农学院，后来独立小来。Davis是一个大学城，很小的城市，Davis校园基本就构成了这个城市。
　　2． quadrupedal andbipedal：quad-：构词词素，是“四”的意思；bi-：构词词素，是“二”的意思； ped-：构词词素，是“脚”的意思；-al是构成形容词的后缀，表示“……的”。因此，quadrupedal 意为“凹足动物的”，bipedal意为“二足动物的”。
　　3． bipedalism：系bipedal(二足动物的)的对应名词，这里后缀-ism表示“特征”、“特性”。

　　练习：
　　1． What did Michael Sockol and his team find out in their study of chimpanzees?
　　A Tile evidence why chimpanzees can be trained to use treadmills．
　　B The evidence why our apelike ancestors came to walk on four legs．
　　C The evidence why our apelike ancestors came to walk on two legs．
　　D The evidence why chimpanzees can be trained to walk on two legs．
　　2． Which of the following best interprets the meaning of “While the chimps worked out ．．．． ” (the first sentence of the third paragraph)?
　　A While the chimps worked in the lab ．．．
　　B While the chimps exercised in the gym ．．．
　　C While the chimps tried to figure out what they should do ．．．
　　D While the chimps tried to understand the instructions ．．．
　　3． What was the result of the finding，according to Paragraph 5?
　　A Three chimps used more energy walking on two legs．
　　B One chimp used less energy walking on two legs．
　　C One chimp used about the same energy walking on two legs as on four．
　　D All of the above．
　　4． What was true of the hypothesis of the research?
　　A Our apelike ancestors were anatomically different but had the same gaits．
　　B Bipeds with natural selection had an advantage over quadruped．
　　C Our apelike ancestors could adapt to different climate changes due to genetic variation．
　　D Bipeds had an advantage over quadrupeds due to changes in the environment．
　　5． What does fossil and molecular evidence tell us about our earliest ancestors?
　　A They experienced more climate changes than we do today．
　　B Due to changes in climate，they were forced to travel between food patches．
　　C They could cover more ground than their quadrupedal peers because they used less energy．
　　D They could travel longer distances on the ground than those who could use less energy．
　　答案与题解：
　　1． C 短文的第一段直接回答了这个问题。
　　2． B worked out在此是“运动，锻炼”的意思，所以选择B。
　　3． D 第五段的第三、第四和第五句提供了答案。bipedalism was more expensive的意思是：两足行走消耗更多的体能。walking upright的意思是：直立行走，即两足行走。
　　4． B 第六段告诉了我们研究的两个假设：猿人祖先在解剖学意义上存在着差异，这一差异影响了它们的步态；这些差异在自然选择的过程中决定了遗传变异，而环境变化使得两足行走的猿人比起四足行走的猿人更有战势。A、C、D都不是正确的说法，只有B在该段中被提到。
　　5． C 倒数第二段提供了问题的答案。travel longer distances用的是比较级，这里是将两足行走的猿人与上文中四足行走的猿人做比较。those who could cover more ground using less energy指的是上文提到的与四足行走的猿人相比，体能消耗较小的两足行走猿人。其他选择都不是正确说法。