Scientists long ago came upon the idea of growing plants in the ocean .（)

(判断)AIDS, fifty years ago, didn’t exist.Fifteen years ago a few doctors and public health officials noticed the first cases.Within a few years it was clear that it has now killed almost 14 million people around the world.

Four years ago doctors came up with the first treatment to make a dent in the spiraling death rate.Today that treatment works for some patients, but it’s not clear how long results will last.And still there is no cure.

For the nearly 35 million people around the world now living with HIV, there may never be a cure.Once cells are infected with HIV, it is very difficult — perhaps impossible ―to rid them of the virus.The only sure way to stop AIDS is to prevent infection in the first place, and only a vaccine can do that.

Unfortunately HIV is one of the most changeable viruses known to science.After more than a dozen years, it is still rather difficult to produce effective vaccine.

Still the billions of dollars spent on AIDS research over the past 20 years has not been wasted.As scientists learn more about how HIV survives in the human body, they are realizing that drugs alone may not be enough.To contain the virus effectively, it may take a balance between drug treatments that can keep HIV levels low and a strengthened immune system that can then target and destroy the remaining virus.Until scientists find a vaccine, however, they may control but never cure the century’s final scourge.

46.AIDS didn’t exist fifteen years ago.

47.Scientists have found a vaccine which can prevent HIV infection.

48.Although some treatment works for some patients with HIV, there is still no cure.

49.HIV is a changeable virus so that it is very difficult to produce effective vaccine.

50.We have wasted billions of dollars on AIDS research.

in the sixteenth century. According to them, the sailors of the ancient world did not explore distant parts of the world; they did not have the necessary knowledge or skills for long sea journeys. However, the people who have this opinion are forgetting two important facts of history.

First, sometimes early scientists have an idea which is correct, but scientists in later centuries do not believe it. For example, about 270 B. C., a Greek scientist had an idea which we all believe today: The earth moves around the sun. But for the following 1,600 years scientists did not believe this. In their opinion, the sun clearly moved around the earth. They discovered the truth again only in the fifteenth century!

The second fact of history that many people forget is this: Ancient does not mean primitive. For example, the ancient Egyptians knew a great deal about the stars; they used this knowledge to find their way across the oceans. Two thousand years ago a Greek scientist who lived in Egypt calculated the distance around the earth. The results of his calculations were close to the real distance we know today! So the ancients had a great deal of scientific knowledge. They also had skills which equaled the skills of to- day. For example, 1,300 years ago and before, fishermen in Ireland built their boats of wood and leather. Today some fishermen in Ireland still make boats of the same de- sign. They use tools and materials which are not very different from the tools and materitals which their ancestors used. Why？ The ancient design of the boats was good, and with skillful sailors, these boats can sail in all kinds of weather.

Clearly long before the sixteenth century, people had the skill, the knowledge and the equipment which were necessary for long journeys by sea. The world did not have to wait until the sixteenth century for its first explorers!

Which of the following statements is consistent with the passage？

A．According to the writer, we only began to really explore the world in the sixteenth century.

B．In the history of science, people sometimes have to discover a fact a second time.

C．The ancient Egyptians had very little knowledge about the stars.

D．The writer agrees with many Americans and Europeans except for the two facts mentioned in the passage.

Questions are based on the following passage．

Most of us are used to seasons． Each year, spring follows winter, which follows autumn, which follows summer, which follows spring． And winter is colder than summer． But the earth goes through temperature cycles over much longer perio~ds than those that we experience． Between 65,000 and 35,000 years ago, the planet was much colder than it is now． During that time the temperature also changed a lot, with periods of warming and cooling． Ice melted duringthe warm periods, which made sea levels rise． Water froze again during the cold periods．

(77) A new study from Switzerland sheds light on where ice sheets melted during the ice age． It now seems that the ice melted at both ends of the earth, rather than just in either northemor southern regions．

age． It now seems that the ice melted at both ends of the earth, rather than just in either northern

or southern regions．

This surprised the researchers from the University of Bern． (78) Scientists have long assumed that most of the ice that melted was in the Northern hemisphere (半球) during the 30,000-year long ice age． That belief was held because the North Pole is surrounded by land, while the South Pole is surrounded by the Antarctic Ocean． It is easier for ice sheets to grow on land． If surrounded by sea the ice can easily just slip into the ocean instead of building up．

The researchers used a computer model to look at ways the ice could melt and how it might affect sea levels． They compared these results to evidence of how temperatures and currents actually changed during that time． The model showed that if it was only in the Northern hemisphere that ice melted, there would have been a bigger impact (影响）on ocean currents (洋流) and sea temperatures than what actually happened． Studies suggest that melting just in the Southern hemisphere would have been impossible, too． The only reasonable conclusion, the scientists could make, was that ice melted equally in the North and the South．

It is still a mystery as to what caused the temperature changes that caused the ice to melt．

The North Pole is surrounded by land， while the South Pole is surrounded by the Antarctic Ocean． So scientists thought that __________ 查看材料

A.most of the ice melted in the Northern hemisphere

B.most of the ice melted in the Southern hemisphere

C.The North Pole is colder than the South Pole

D.The South Pole is colder than the North Pole

monly known as Megalodon, is believed to have lived between I million and 5 million years ago and thought to have been 52 feet long. It is (or was) a shark that had a jaw 7 or more feet wide. Fairly recently, there has been some speculation about whether it is extinct or just out of reach. But few people believe that Megalodon has found a home deep in the ocean.

There are many known "Living Fossils": Coelacanth, Sea Cucumbers, Sea Urchins, Lobsters, Sea Stars. The common ones like lobsters and sea urchins are not really looked on as anything amazing. They've been around for thousands of years or more, and axe easily accessible to us. What if they weren't accessible and yet still existed？ We would label them extinct. The discovery of a live Coelacanth, a fish long believed extinct, challenged some scientists' long-held beliefs on extinction. There have been recent discoveries Of incredibly large squid, and deep-sea fish never before seen by scientists.

In the 1960s the U.S. Navy set up underwater microphones around the world to track Soviet submarines. The network, known as the Sound Surveillance System, still lies deep below the ocean's surface in a layer of water known as the "deep sound channel'. The temperature and pressure of the channel allow sound waves to travel undisturbed. NOAA's Acoustic Monitoring Project has been using the Sound Surveillance System to listen for changes in ocean structure like ocean currents or volcanic activity. Most of the sounds recorded are common and of no concern. One sound, identified in 1977 by U.S. Navy "spy" sensors, was odd. It was obviously a marine animal but the call was more powerful than any of the calls made by any other reported sea creature. It was too big for a whale. Could it be a deep-sea monster？ One possibility was a giant squid, but no one is sure. It was named "Bloop". Could it be Megalodon？ If Megalodon is still alive down in the bottom of the ocean, we may some day soon discover it. Then what？ Deep sea diving will never be the same, that's for sure!

The following is commonly known EXCEPT ________.

A．Megalodon, the largest shark, is extinct

B．Megalodon is not extinct but just out of reach

C．Megalodon was 52 feet long and had a jaw 7 or more feet wide

D．Megalodnn lived between several million years ago

s people today act younger than their parents did at the same age.

Scientists have defined a new age concept and believe it could explain why populations are aging, but at the same time seem to be getting younger.

Instead of measuring aging by how long people have lived, the scientists have factored in how many more years people can probably still look forward to.

"Using that measure, the average person can get younger in the sense that he or she can have even more years to live as time goes on," said Warren Sanderson of the University of New York in Stony Brook.

He and Sergei Scherbov of the Vienna lnstitute of Demography (人口统计学) at the Austrian (奥地利的) Academy of Sciences, have used their method to estimate how the proportion of elderly people in Germany, Japan and the United States will change in the future.

The average German was 39.9 years old in 2000 and could plan to live for another 39.2 years, according to research reported in the journal Nature on Wednesday.

However, by 2050 the average German will be 51.9 years old and will be expected to live another 37.1 years. So middle age in 2050 would occur at around 52 years instead of 40 years as in 2000.

"As people have more and more years to live they have to save more and plan more and they effectively are behaving as if they were younger," said Sanderson.

Five years ago, the average American was 35.3 years old and could plan for 43.5 more years of life. By 2050, the researchers estimate it will increase to 41.7 years and 45.8 future years.

"A lot of our ski/Is, our education, our savings and the way we dear with our health care depend a great deal on how many years we have to live," said Sanderson.

This dimension of how many years people have to live has been completely ignored in the discussion of aging so far.

第36题：People 40 years of age today seem to be as young as

A．their parents were at the same age.

B．their parents were at the age of 30.

C．their children will be at the same age.

D．their children will be at the age of 30.

on life.A.advanced B.relieved C.produced D.thrust

A.Long ago

B.Long before

C.About one month

D.Once a year