more efficiently.they stopped to have a coffee break．( )A．WorkingB．To workC．WorkD．Worked 题目和参考答案——青夏教育精英家教网—

题目内容

20．______ more efficiently，they stopped to have a coffee break．（　　）

A．

Working

B．

To work

C．

Work

D．

Worked

分析为了工作更有效率，他们停下来喝杯咖啡休息一下．

解答答案：B 题干中有逗号分隔，没有连词，要用非谓语动词；work与主语they之间是主动关系；句意表达的是目的，是一个目的状语，不是表示伴随动作，要用动词不等式表示．故选B．

点评动词不等式是非谓语动词的一种，也是英语中比较活跃的一类结构．通常用来作主语，宾语，表语，定语，状语等．学习时要全面掌握，熟练运用．

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Hummingbirds (蜂鸟) are one of nature’s most energetic fliers and the only birds to hover in the air by relying on their strength alone.

Now scientists have found that it is the ratio (比值) of the bird’s wing length to its width that makes them so efficient. The discovery is helping experts compete with 42 million years of natural selection to build helicopters that are increasingly efficient.

David Lentink, an assistant professor at Stanford University in California, tested wings from 12 different species of hummingbirds, which he sourced from museums. He placed them on a machine used to test the aerodynamics (气力学) of the helicopter blades (桨叶). Professor Lentink’s team used the same machine to test the blades from an advanced micro-helicopter used by the UK’s army. They found that the micro-helicopter’s blades are as efficient at hovering as the average hummingbirds.

But while the micro-helicopter’s blades kept pace with the average hummingbird wings, they could not keep up with the most efficient hummingbird’s wing. The wings of Anna’s hummingbird were found to be about 27 percent more efficient than the man-made micro- helicopter’s blades.

While Professor Lentink wasn’t surprised at nature’s superiority, he said that helicopter blades have come a long way. “The technology is at the level of an average hummingbird,” he said. “A helicopter is really the most efficient hovering device that we can build. The best hummingbirds are still better, but I think it’s amazing that we’re getting closer. It’s not easy to match their performance, but if we build better wings with better shapes, we might match hummingbirds.”

Professor Lentink said that we don’t know how hummingbirds maintain their flight in a strong wind, how they navigate (确定方向) through branches, or how they change direction so quickly. He thinks that great steps could be made by studying wing aspect ratios—the ratio of wing length to wing width. Understanding these abilities and characteristics could be a benefit for robotics and will be the focus of future experiments.

1.What did the scientists find about hummingbirds?

A. Their wings are long and wide.

B. They can hover in the air for a long time.

C. The ratio of their wing length to wing width is very important.

D. They are the most energetic flier in nature.

2.Which is the right order of Professor Lentink’s research?

① Tested wings from different species of hummingbirds.

② Got resources from museums.

③ Analyzed the results and drew a conclusion.

④ Tested the blades from a micro-helicopter.

A. ①②③④ B. ②①③④ C. ②④①③ D. ②①④③

3.According to Professor Lentink, what will be the focus of future experiments?