Laser-doppler radar is especially valuable in space missions because ______. ()
A.it is one thousand times more precise than microwave radar
B.it provides precise measures of the velocity of space vehicles
C.it is a new system of radar
D.it can measure the movement of a spaceship less accurately than a microwave radar
The article suggests that______.
A. our earth exists before the sun
B. how space formed
C. no one knows where the earth comes from
D. our earth used to be part of a high mountain on the sun
According to the passage, visitors from space may have landed on the earth ______.
A.long before man had dreamed of it
B.long before there were human beings
C.in the last few hundred years
D.after the space age began
The model has shown that this radar system, known as laser-doppler radar, can measure with absolute precision speeds varying from spaceship orbital injection (进入) velocities (速度) of five miles per second down to virtual stops--speeds of less than one ten thousandth of an inch per second. According to the scientists who are developing this system, such fine measures of velocity are of prime importance in space missions. In a rendezvous (对接) between two spaceships, or in a landing approach by a vehicle onto an orbiting space station, a bump could rip open a ship's skin, or a nudge could knock the station out of its orbit.
The light-beam radar, which operates at a frequency of trillions (百万兆) of cycles per second, could easily detect and measure the movement of a vehicle edging up to a satellite space station. A control system using so precise a signal as this would allow a huge vehicle to dock at a space station as lightly as a feather.
Laser-doppler radar ______. ()
A.measures the movements of a spaceship by means of light beam
B.makes use of microwaves
C.makes use of sound waves
D.Both A and B
We believe, however, that some two thousand million years ago, another star wandering through space, happened to come near our sun. Just as the sun and the moon raise tides on the earth, so this star must have raised tides on the surface of the sun. But they were very different from the small tides that are raised in our oceans; a large tidal wave' must have travelled over the surface of the sun, at last forming a mountain so high that we cannot imagine it. As the cause of the disturbance (动荡) came nearer, so the mountain rose higher and higher. And before the star began to move away again, its tidal pull had become so powerful that this mountain was torn to pieces and threw off small parts of itself into space. These small pieces have been going round the sun ever since. They are the planets (行星).
Millions of stars are______.
A.following a regular path in space
B.always travelling together
C.seldom wandering about in the universe
D.moving about without a fixed course
Food for space has to be packed in special ways. Some of it goes into tubes that a man can squeeze into his mouth. Bite-sized cookies are packed in plastic.
There is a good reason for covering each bite. The plastic keeps pieces of food from travelling in the spaceship. On the earth very small pieces of food would simply fall to the floor. But gravity doesn' t pull them to the floor when they are out of the plastic in a spaceship. (78) They move here and there and can get into a man' s eyes or into the spaceship' s instruments. If any of the instruments is blocked, the astronauts may have trouble getting safely home.
As astronauts travel on longer space trips, he must take time to sleep. An astronaut can fit himself to his seat with a kind of seat belt. Or, if he wants to, he can sleep in a sleeping bag which is fixed in place under his seat. But be careful he must put his hands under the belt when he goes to sleep. This is because he is really afraid that he might touch one of controls that isn' t supposed to be touched until later.
Why would astronauts cover each bite of food in space?
A.Because small pieces of food would fall down to the floor.
B.Because weightless pieces of food might make trouble when they travel around.
C.Because they haven' t enough food for longer trips.
D.Because astronauts don' t want to waste food.
Five hundred years ago, news of important happenings--battles lost and won, kings or rulers overthrown or killed--took months and even years to travel from one country to another. The news passed by word of mouth and was never accurate. Today we can read in our newspapers of important e vents that occur in faraway countries on the same day they happen.
Apart from supplying news from all over the world, newspapers give us a lot of other useful in formation. There are weather reports, radio, television and film guides, book reviews, stories, and, of course, advertisements. There are all sorts of advertisements. The bigger ones are put in by large companies to bring attention to their products. They pay the newspapers thousands of dollars for their advertising space, but it is worth the money, for news of their products goes into almost every home in the country. For those who produce newspapers, advertisements are also important. Money earned from advertisements makes it possible for them to sell their newspapers at a low price and still make a profit.
The habit of reading newspapers is ______.
A.widespread
B.found among a few families
C.not popular
D.uncommon
Asteroids are different forms of the meteoroids that race across the night sky. Most orbits the sun far from Earth and don't threaten us. But there are also thousands of asteroids whose orbits put them on a violent coming course together with Earth.
Buy $ 50 million worth of new telescopes right now. Then spend $10 mil]ion a year for the next 25 years to locate most of the space rocks. By the time we spot a fatal one, the scientists say, we'll have a way to change its course.
Some scientists favor pushing asteroids off course with nuclear weapons. But the cost wouldn't be cheap.
Is it worth it? Two things experts consider when judging any risk are: 1) How likely the event is; and 2) How bad the consequences if the event occurs. Experts think asteroids big enough to destroy lots of life might strike Earth once every 500,000 years. Sounds pretty rare but if one did fall it would be the end of the world. "If we don't take care of these big asteroids, they'll take care of us. "Says one scientist. "Its that simple."
The cure, though, might be worse than the disease, Do we really want fleets of nuclear weapons silting around on Earth? "The world has less to fear from doomsday rocks than from a great nuclear fleet set against them. "Said a New York Times article.
What does the passage say about asteroids and meteoroids?
A.They are heavenly bodies similar in nature.
B.There are more asteroids than meteoroids.
C.They are heavenly bodies different in composition.
D.Asteroids are more mysterious than meteoroids.
(66)
A.passes
B.goes
C.flashes
D.moves
In a plan called “Station Renaissance” that it__3__in November, JR East said that it would__4__using its commercial spaces for shops and restaurants, extending them to__5__more suitable for the information age. It wants train stations as pick-up__6__for such goods as books, flowers and groceries__7__over the Internet. In a country where city__8__depend heavily on trains__9__commuting, about 16 million people a day go to its train stations anyway, the company __10__. So, picking up commodities at train stations__11__consumers extra travel and missed home deliveries. JR East already has been using its station__12__stores for this purpose, but it plans to create__13__spaces for the delivery of Internet goods.
The company also plans to introduce __14__cards—known in Japan as IC cards because they use integrated circuit for__15__information__16__ train tickets and commuter passes__17__the magnetic ones used today, integrating them into a/an __18__pass. This will save the company money, because__19__for IC cards are much less expensive than magnetic systems. Increased use of IC cards should also__20__the space needed for ticket vending.
A.perspectives
B.outlooks
C.prospects
D.spectacles
Life on Mars
Perhaps more than anything else, scientists are eager to find out if Martian life existed in the past—or still exists.【61】telescopes first zoomed in【62】Mars in the 17th century, people have conjured up a wild【63】of images or what Martians might look like. But space probes like the 1997 Sojourner land rover have yielded no evidence of such alien beings.
Most experts agree that if life did at one time evolve on Mars, finding evidence of that life—which would likely take the form. of tiny organisms—won't be easy.【64】, many scientists are optimistic. "We've got organisms on Earth that adapted to life deep【65】the surface in underground water wells, " says Stephen Clifford. "【66】life like that evolved on Mars four billion years ago, there's no reason why it【67】today. "
【68】last year's disappointing losses, the future of Martian exploration looks【69】This year, two major
films about fictitious Mars missions—Red Planet and Missions to Mars—are certain to heighten interest in our planetary neighbour. More important, plans for new sets of NASA orbiters and landers—one to launch in 2001 , the other in 2003—are already in the works. Without a doubt, each new mission will inch scientists closer to【70】the mysteries of planet Mars.
(61)
A.When
B.Before
C.Ever since
D.Ever