With his attention________on the shops along the roadside，he knocked an old man down while riding to school.

A  concentrating     B．concentrated     C．to concentrate      D．concentrates

答案　B

解析　考查詞組，故選B項(xiàng)。

D
　　In the atmosphere,carbon dioxide actd rather like a one-way mirror or the glass in the roof of a greenhouse which allows the sun's rays to enter but prevents the heat from excaping.
　　According to a weather expert's prediction,the atmosphere will be 3 warmer in the year 2050 than it is today, if man continues to burn luels at the present rate. If this warming up took place,the ice caps in the poles would begin to melt,thus raising sea level several meters and severely flooding coastal cities.Also，the increase in atmospheric temperature would lead to great changes in the climate of the northern hemisphere(半球),psooicbly resulting in an alteration of earth's chief food growing zones.
　　In the past,concern about a man - made warming of the earth has concentrated on the Arctic because the Antarctic is much colder and has a much thicker ice sheet.But the weather experts are now paying more attention to West Antarctic,which may be affected by a warming on the scale that will possibly take place in the next fifty years from on burning of fuels.
　　Satellite pictures showthat large areas of Antarctic ice are already disappearing.The evidence available suggests that a warming has taken place.This fits the theory that carbon dioxide warms the earth.
　　However,most of the fuel is burnt in the northern hemisphere,where temperatures seem to be falling.Scientists conclude,therefore,that up to now natural influences on the weather have exceeded those caused by man.The question is:Which natural cause has most effect on the weather?
　　One possibility is the variable behavior of the sun.Astronomers at one research station have studied the hot spots and cold spots(that is,the relatively less hot spots) on the sun. As the sun rotates(旋轉(zhuǎn)),every 27.5 days,it presents hotter or colder faces to the earth,and different aspects to different parts of the earth.This seems to have a considerable effect on the distribution of the earth's atmospheric pressure,and consequently on wind circulation.The sun is also variable over a long term:its heat output goes up and down in cycles,the latest trend being downward.
　　Scientists are now finding mutual relations between models of solar weather interactions and the actual climate over many thousands of years ,including the last Ice Age.The problem is that the models are predicting that the world should be entering a new Ice Age and it is not.
　　One way of solving this theoretical difficulty is to assume a delay of thousands of years while the solar effects overcome the inertia(不活動(dòng)，惰性) of the earth's climate.If this is right,the warming effect of carbon dioxide might thus be serving as a useful counter balance to the sun's diminishing heat.
　　68.It can be concluded that a concentration of carbon dioxide in the atmosphere would ___.
　　　A.mean a warming - up im the Arctic
　　　B.raise the temperature of the earth's surface
　　　C.prevent the sun's rays from reaching the earth's surface
　　　D.account for great changes in the climate in the northern hemiphere
　　69.Although the fuel consumption is greater in the northern hemisphere,temperatures there seem to be falling.This is _______.
　　　A.mainly because the levels of carbon dioxide are rising
　　　B.partly due to variations in the output of solar energy
　　　C.possibly because the ice caps in the poles are melting
　　　D.exclusively due to the effect of the inertia of the earth's climate
　　70.On the basis of their models,scientists are of the opinion that ________.
　　　A.the climate of the world should be becoming cooler
　　　B.the new Ice Age will be delayed by the greenhouse effect
　　　C.the man - made warming effect helps to increase the solar effects
　　　D.it will take thousands of years for the inertia of the earth's climate to take effect

In 1883, an imaginative engineer named John Roebling decided to build a spectacular bridge connecting New York with Long Island. However, bridge building experts throughout the world thought that this was a pipe dream. It was not practical. It had never been done before.

But Roebling refused to listen to them. He thought about the bridge day and night and he knew deep in his heart that it could be done. After much discussion and persuasion he convinced his son Washington, who was a promising engineer himself, that the bridge in fact could be built.

Working together for the first time, the father and son developed concepts of how it could be accomplished. With great excitement, they hired their crew and began to build their dream bridge.

The project started well, but several months after it began, a tragic accident on the site took the life of John Roebling. Washington was so seriously injured that he was never able to walk, talk or even move again.

"We told them so", "Crazy men and their crazy dreams", "It's foolish to chase wild visions", the critics said and most thought the project should be scrapped since the Roeblings were the only ones who knew how the bridge could be built. In spite of his handicap Washington still had a burning desire to complete the bridge and his mind was still as sharp as ever.

Washington's wife tried to inspire and pass on her husband's enthusiasm to some of his friends, but they were too daunted by the task. As he lay in his hospital room, an idea suddenly hit him. All he could do was move one finger and he decided to make the best use of it. By moving this finger and tapping it on his wife's arm, he slowly developed a code to communicate with her. Then he used this method to tell his wife what the engineers should do. It seemed crazy but the project was under way again. For 13 years Washington tapped out his instructions with his finger on his wife's arm, until the bridge was finally completed.

Today the spectacular Brooklyn Bridge stands in all its glory as a tribute to the triumph of one man's spirit and his determination not to be defeated by circumstances.

_ What did most people think about Roebling's idea to build the bridge?

A. It would never become a reality.                    B. Washington was not experienced enough.

C. It would take a lot of time.                            D. Finding the money would be impossible. 

_The underlined word `daunted' (para. 6) is closest in meaning to '______'.

  A. unpleasant    B. scared    C. amazed    D. determined

_ Which of the following shows the correct order of the events that happened in the story?

   a. Roebling convinced his son.

   b. Washington found a new way to communicate.

   c. They hired the crew.

d. The bridge was completed.

   e. Roebling wanted to build a bridge.

   f. There was a tragic accident.

A. e, a, c, f, d, b     B. e, a, f, b, c, d    C. e, f, a, b, c, d    D. e, a, c, f, b, d　　

_ What can we learn about Washington's wife?

A. She knew sign language very well.

B. She was devoted to her husband.

C. She developed a code to communicate with her husband.

D. She helped her husband design the plan.

_ What does the story tell us?

  A. Success will come with the passing of time.

  B. Struggles are exactly what we need in our lives.

  C. Even the most distant dream can be realised with a never-say-die attitude.

  D. The people who make a difference in our life should be remembered forever.