The picture _______ on the wall is painted by my nephew.

A. having hung      B. hanging

C. hangs  D. being hung

We looked everywhere for the keys, but they are nowhere _______.

A. to find       B. to have found

C. to be found D. being found

A black hole is created when a large star burns out. Like our sun, stars are unbelievably hot furnaces(熔炉) that burn their own matter as fuel. When most of the fuel is used up, the star begins to die.

The death of a star is not a quiet event. First there is a huge explosion. As its outer layer is blasted off into space, the dying star shines as brightly as a billion suns.

After the explosion gravity pulls in what’s left of the star. As the outside of the star sinks toward the center, the star gets smaller and smaller. The material the star is made of becomes tightly packed together. A star is so dense that a teaspoon of matter from it weighs billion of pounds.

The more the star shrinks, the stronger the gravity inside it becomes. Soon the star is very tiny, and the gravity pulling it in is unbelievably strong. In fact, the gravity is so strong that it even pulls light into the star! Since all the light is pulled in, none can go out. The star becomes black when there is no light. Then a black hole is born!

That’s what we know about black holes. What we don’t know is this: What happens inside a black hole after the star has been squeezed into a tiny ball? Does it keep getting smaller and smaller forever? Such a possibility is hard to imagine.

But if the black hole doesn’t keep shrinking, what happens to it? Some scientists think black holes are like doorways to another world．They say that as the star disappears from our universe, it goes into another universe. In other words a black hole in our universe could turn into a “white hole” in a different universe. As the black hole swallows light, the white hole shines brightly — somewhere else. But where? A different place, perhaps, or a different time — many years in the past or future.

Could you travel through a black hole? Right now, no. Nothing we know of could go into a black hole without being crushed．So far the time being, black hole must remain a mystery.

Black holes are a mystery—but that hasn’t stopped scientists from dreaming about them. One scientist suggested that in the future we might make use of the power of black holes. They would supply all of Earth’s energy needs, with plenty to spare. Another scientist wondered if a black hole could some day be used to swallow earthly waste—a sort of huge waste disposal (处理) in the sky!

When the star begins to die ______.

       A．there is no fuel left in it B．its outer layer goes into space first

       C．a huge explosion will happen        D．it doesn’t give off light any longer

Which of the following doesn’t help produce a black hole?

       A．The gravity inside the star is very strong.

       B．The light can’t go out of the star.

       C．The star becomes smaller and smaller

       D．The dying star shines very brightly.

The black hole ______.

       A．continues becoming smaller and smaller all the time

       B．goes into another universe and becomes a white hole

       C．can pull in everything we know of in the world

       D．will appear at another place at a different time

What’s the best title for this passage?

       A．A New Scientific Discovery: Black Holes

       B．How Do Black Holes Come Into Being?

       C．What Are Black Holes?

       D．Travel Through A Black Hole

A "lost tribe" that reached America from Australia may have been the first Native Americans, according to a new theory.

If proved by DNA evidence, the theory will break long established beliefs about the southerly migration of people who entered America across the Bering Strait, found it empty and occupied it.

On this theory rests the belief of Native Americans to have been the first true Americans. They would be classified to the ranks of escapee, beaten to the New World by Aboriginals (土著人) in boats.

To a European, this may seem like an academic argument, but to Americans it is a philosophical question about identity (身份), Silvia Gonzales, of Liverpool University said .

Her claims are based on skeletons found in the California Peninsula of Mexico that have skulls (头骨) quite unlike the broad Mongolian features of Native Americans. These narrow-skulled people have more in common with southern Asians, Aboriginal Australians and people of the South Pacific Region.

The bones, stored at the National Museum of Anthropology (人类学) in Mexico City, have been carbon-dated and one is 12,700 years old, which places it several thousand years before the arrival of people from the North. "We think there were several migration waves into the Americas at different times by different human groups," Dr. Gonzales said． "The timing, route and point of origin of the first colonization of the Americas remains a most contentious topic in human evolution."

But comparisons based on skull shape are not considered conclusive by anthropologists, so a team of Mexican and British scientists, backed by the Natural Environment Research Council, has also attempted to take out DNA from the bones. Dr. Gonzales declined yesterday to say exactly what the results were, as they need to be checked, but indicated that they were consistent（一致） with an Australian origin.

It is generally considered that the first Native Americans came from _____.

       A．North Asia      B．Australia   C．South Pacific   D．South Asia

The skeletons found in the California Peninsula of Mexico have _____.

       A．the broad skull shape     

       B．the narrow skull shape

       C．different features of Aboriginal Australians   

       D．the same features of Native Americans

The underlined “contentious” is similar in meaning to “_____”.

       A．likely to cause great interest    B．difficult to solve

       C．well-known to all           D． likely to cause argument

Which of the following statements is true according to the text?

       A．Research on skulls can draw an exact conclusion.

       B．DNA tests have proved the fact that the first Native Americans came from Australian.

       C．Scientists are still not sure about the origin of the Native Americans.

       D．People began to enter America across the Bering Strait about 12,700 years ago.

In recent years many countries of the world have been faced with the problem of how to make their workers more productive. Some experts claim the answer is to make jobs more varied. But do more various jobs lead to greater productivity? There are facts to suggest that while variety certainly makes the worker's life more enjoyable, it does not actually make him work harder. As far as increasing productivity is concerned, then variety is not an important factor.

Other experts feel that giving the worker freedom to do his job in his own way is important, and there is no doubt that this is true. The problem is that this kind of freedom cannot easily be given in the modern factory with its complicated machinery that must be used in a fixed way. Thus while freedom of choice may be important, there is usually very little that can be done to create it.

Another very important consideration is how each worker contributes to the product he is making. In most factories the worker sees only one part of the product. Some car factories are now experimenting with having many small production lines rather than one large one, so that each worker contributes more to the production of the cars on his line. It would seem that not only is degree of the worker’s contribution an important factor, therefore, but it is also one we can do something about.

To what degree does more money lead to greater productivity? The workers themselves certainly think this is important. Maybe they want more money only because the work they do is boring. Money just lets them enjoy their spare time more. A similar argument may explain demands for shorter working hours. Perhaps if we succeed in making their jobs more interesting, they will neither want more money, nor will shorter working hours be so important to them.

Which of the following is the best way to make workers work harder according to the author?

A．Increasing their pay.

B．Giving them more spare time.

C．Making the work itself meaningful.

D．Replacing large production lines with small ones.

The reason why a worker cannot have freedom in doing the job in his own way is that ___  .

A．the machine is so badly needed that more of it should be bought

B．there are e production lines in factories

C．the bosses can create very little freedom of choices

D．the machines must be operated strictly according to instructions and rules

Besides money, what may make workers work more actively?

A. extra free hours     B. More comfort of life

C. interesting jobs      D. better working conditions

The best title for this passage may be _______.

A．Problems of Modern Workers            B．Making Jobs More Interesting

C．Pushing Workers to Produce More        D．How to Improve Labor Productivity

The ____ is that the new machine will arrive tomorrow.

A. chance     B. luck       C. happening    D. accident

---What do you think of my suggestion?

--- Sorry. What's that? I ____ about something else.

A. thought    B. am thinking  C. was thinking D. had thought

---I went to the beach and got plenty of rest.

--- _____ You looked tired last time I saw you.

A. I had hoped so.  B.Really?

C. I m glad you did.  D. That sounds a good idea.

Doing your homework is a sure way to improve yor test scores, and this is especially true ____ it comes to classroom tests.

A. before     B. since    C. when   D. after

I'll be home late, but please don't stay ____ for me.

A. up    B. in    C. over      D. on