How genes could cause a potential problem for conservationists.How genes could cause a potential problem for conservationists.

How genes could cause a potential problem for conservationists.

Broadsides could be published with little risk to colonial printers because they

A．required a small financial investment and sold quickly

B．were in great demand in European markets

C．were more popular with colonists than chapbooks and pamphlets

D．generally dealt with topics of long-term interest to many colonists

Broadsides could be published with little risk to colonial printers because they

A．required a small financial investment and sold quickly

B．were in great demand in European markets

C．were more popular with colonists than chapbooks and pamphlets

D．generally dealt with topics of long-term interest to many colonists

For many years, scientists couldn't figure out how atoms and molecules combined to make living things. Plants, fish, dinosaurs, and people are made of atoms and molecules, but they are put together in a more complicated way than the molecules in the primitive ocean. What's more, living things have energy and can reproduce, while the chemicals on the Earth 4 billion years ago were lifeless.

After years of study, scientists figured out that living things, including human bodies, are basically made of amino acids, nucleotide bases, lipids and water. How could such complicated molecules have been formed and have started to interact in the primitive soup? Scientists were stumped.

Then, in 1953, two scientists named Harold Urey and Stanley L. Miller did a very simple experiment to find out what had happened on the primitive Earth. They set up some tubes and bottles in a closed loop, and put in some of the same gases that were present in the atmosphere 4 billion years ago—water vapour, ammonia, carbon dioxide, methane, and hydrogen.

Then they shot an electric spark through the gases to simulate bolts of lightning on the ancient Earth, circulated the gases through some water, sent them back for more sparks, and so on. After several days, the water that the gases had been bubbling through turned brown. Some new chemicals were dissolved in it. When Miller and Urey analyzed the liquid, they found that it contained amino acids—the very kind of molecules found in all living things.

When did scientists come to realize how the atoms and molecules on the Earth mostlikely combined to make living things?

A．4 billion years ago.

B．After seven days.

C．Many years ago.

D．In 1953.

A．Because books could be lent to everyone.

B．Because books could be lent at no costs.

C．Because books were lent to students and faculty.

D．Because books were lent on a paid membership basis.

A．Books could be lent to everyone.

B．Books could be lent by book stores.

C．Books were lent to students and the faculty.

D．Books were lent on a membership basis.

A．The graduate students could understand the lecture.

B．The undergraduate students could understand the lecture.

C．Both the undergraduate and the graduate students understand the lecture.

D．Neither the undergraduate nor the graduate students could understand the lecture.

Why They Came

Not many decisions could have been more difficult for a family to make them to say farewell to a community where it had lived for centuries, to abandon old ties and familiar landmarks, and to sail across dark seas to a strange land. Today, when mass communications tell one part of the world all about another, it is quite easy to understand how poverty or tyranny might force people to exchange an old nation for a new one. But centuries ago migration was a leap into the unknown. It was an enormous intellectual and emotional commitment. The forces that moved early immigrants to their great decision — the decision to leave their homes and begin an adventure filled with uncertainty, risk and hardship — must have been of overpowering proportions. As Oscar Handlin states, the early immigrants of America "would collide with unaccustomed problems, learn to understand alien ways and alien languages, manage to survive in a very foreign environment".

Despite the obstacles and uncertainties that lay ahead of them, millions did migrate to "the promised land" — America. But what was it that moved so many to migrate against such overwhelming odds? There were probably as many reasons for coming to America as there were people who came. It was a highly individual decision. Yet it can be said that three large forces—religious persecution, political oppression and economic hardship-provided the chief motives for the mass migrations to America. They were responding in their own way to the pledge of the Declaration of Independence: the promise of "life, liberty and the pursuit of happiness".

The search for freedom of worship has brought people to America from the days of the pilgrims to modern times. In 1620, for example, the Mayflower carried a cargo of 102 passengers who "welcomed the opportunity to advance the gospel of Christ in these remote parts". A number of other groups such as the Jews and Quakers came to America after the Pilgrims, all seeking religious freedom. In more recent times, anti-Semitic persecution in Hitler's Germany has driven people from their homes to seek refuge in America. However, not all religious sects have received the tolerance and understanding for which they came. The Puritans of the Massachusetts Bay Colony showed as little tolerance for dissention beliefs as the Anglicans of England had shown them. They quickly expelled other religious groups from their society. Minority religious sects, from the Quakers and Shakers through the Catholics and Jews to the Mormons, have at various times suffered both discrimination and hostility in the United States.

But the diversity of religious belief has made for religious toleration. In demanding freedom for itself, each sect had to permit freedom for others. The insistence of each successive wave of immigrants upon its right to practice its religion helped make freedom of worship a central part of the American Creed. People who gambled their lives on the right to believe in their own God would not easily surrender that right in a new society.

The second great force behind immigration has been political oppression. America has always been a refuge from tyranny. As a nation conceived in liberty, it has help out to the world the promise of respect for the rights of man. Every time a revolution has failed in Europe, every time a nation has succumbed to tyranny, men and women who love freedom have assembled their families and their belongings and set sail across the seas. This process has not come to an end in our own day. The terrors of Hitler's Germany and Mussolini's Italy, the terrible wars of Southeast Asia — all have brought new thousands seeking safety in the United States.

The economic factor has been more complex than the religious and political factors. From the very beginning, some have come to America in search of riches, some in flight from poverty, and some because t

A．searching for religious freedom

B．breaking with past cultural inheritance

C．escaping political oppression

D．searching for riches

What did he do all this for.

A．To know if animals like chickens could be posted.

B．To amuse the reader with an unlikely answer to the chicken-or-egg puzzle.

C．To know if eggs would break on the way to their destination.

D．To show that he was highly intelligent.

Regeneration of Limbs

Most people would agree that it would be wonderful if humans could regenerate limbs. These who have lost their arms or legs would be complete again. The day is still far off when this might happen. But in the last 10 years, doctors have reported regeneration in smaller parts of the body, most often fingers.

Regeneration is not a newly-discovered process. For centuries, scientists have seen it work in some kinds of animals. Break off a lizard's (蜥蜴的) tail, for example, and it will grow a new tail. Scientists now are looking for a way to turn on this exciting ability in more highly-developed animals, including humans. Their experiments show that nerves, cell chemistry and the natural electric currents in the body all seem to have a part in this process.

The body of every animal contains general purpose cells that change into whatever kind of cells the body needs. Animals such as the lizard or salamander (蝾螈) use these cells to regenerate a new tail or leg when the old one is broken off. These cells collect around the wound. They form. a mass called a blastama (胚基). The cells of the blastema begin to change. Some become bone cells, some muscle cells, some skin cells. Slowly, a new part regrows from the body outward. When completed, the new part is just like the old one.

Mote than 200 years ago, Italian scientist Luigi Spallanzani showed that younger animals have a greater ability to regenerate lost parts than older animals. So do animals lower on the ladder of evolutionary development. The major difference seems to be that less-developed animals have more nerves in their tails and legs than humans do in their arms and legs.

Another helpful piece of information was discovered in the late 1600s. Scientists found that when a creature is injured, an electrical current flows around the wound. The strength of the current depends on how severe the wound is and on how much nerve tissue is present.

In 1945, American scientist Meryl Rose tested another idea about regeneration. He thought a new limb might grow only from an open wound. Doctor Rose cut off the front legs of some frogs, below the knee. He kept the wounds wet with a strong salty liquid. This prevented skin from growing over the wounds. The results were surprising. Frogs do not regenerate new legs naturally. But these frogs began to grow new limbs. About half of each cut-off leg grew back again. New bones and muscles developed.

This research has led doctors to new ways of treating cut-off fingers. Doctors have observed, for example, that many children and some adults will regrow the top of a finger if the wound is left open.

The passage indicates that

A．humans can never regenerate limbs.

B．humans might be able to regenerate limbs in the future.

C．human limbs may be regenerated on some animals first.

D．regeneration of human limbs will soon become a reality.