单选题The meaning is still obscure .

单选题This is the first research finding about the planets with a chance for life.

单选题 下面有3篇短文，每篇短文后有5道题，每道题后面有4个选项。请根据文章的内容，从每题所给的4个选项中选择1个最佳答案。{{B}}第一篇{{/B}} {{B}} Eta Carinae{{/B}} As possibly the galaxy's (银河) most massive star, Eta Carinae is now engaging in some very unusual behaviour. Australian astronomers, being in the Southern Hemisphere (半球), are able to observe it clearly. In the 19th century, Eta Carinae was for a time the third brightest star in the sky. It has now become less bright so that binoculars (双筒望远镜) are needed to see it. "It seems to be brightening and becoming less bright over a period of many years", said Dr Bob Duncan from the Australia Telescope National Facility. While it is not unusual for stars to vary in brightness, the period is usually much shorter. "Since 1992 it has become four times brighter, and then last year it began to drop dramatically," he said. The problem in observing Eta Carinae is that it has been surrounded by a cloud of gas and dust, making it hard to see the star directly. However, radio waves and infrared light (红外线) can pass through this cloud, so telescopes that receive these wavelengths can observe what is occurring. Eta Carinae is of particular interest to astronomers because it seems to be in its death throes (剧痛). Being so large it will end up as a supernova (超新星). There has not been a supernova in our galaxy since the invention of the telescope. While a 1987 explosion in a nearby galaxy gave astronomers plenty of valuable data, they are hungry for an even closer look. Eta Carinae has other unique features, and is the only star known to produce an ultraviolet (紫外线) laser that is brighter than that produced by the Sun. Lasers have been observed in other frequencies from a few stars.

单选题The Greatest Mystery of Whales The whale is a warm-blooded, air-breathing animal, giving birth to its young alive, sucking them—and, like all mammals, originated on land. There are many 1 of this. Its front flippers (鳍状肢), used for steering and stability, are traces of feet. Immense strength is 2 into the great body of the big whales, and in fact most of a whale"s body is one gigantic muscle. The blue whale"s pulling strength has been estimated 3 400 horsepower. One specimen was reported to have towed (拖) a whaling vessel for seven hours at the 4 of eight knot (节). An angry whale will 5 . A famous example of this was the fate of Whaler Essex, 6 was sunk off the coast of South America early in the last century. More recently, steel ships have 7 their plates buckled (使弯曲) in the same way. Sperm whales (抹香鲸) were known to seize the old-time whaleboats in their jaws and crush them. The greatest 8 of whales is their diving ability. The sperm whale dives to the bottom for his 9 food, the octopus (章鱼). In that search he is known to go as far down as 3,200 feet, where the 10 is 1,400 pounds to a square inch. Doing so he will 11 underwater as long as one hour. Two special skills are involved in this storing up enough 12 (all whales are air-breathed)and tolerating the great change in pressure. Just how he does it scientists have not 13 . It is believed that some of the oxygen is stored in a special 14 of blood vessels, rather than just held in the lungs. And it is believed that a special kind of oil in his head is some sort of a compensating mechanism that 15 adjusts the internal pressure of his body. But since you can"t bring a live whale into the laboratory for study, no one knows just how these things work.

单选题Photojournalist Margaret White became famous for her Ucoverage/U of significant events during the Second World War.

单选题The Smog (烟雾) For over a month, Indonesia was in crisis. Forest fires raged out of control as the country suffered its worst drought for 50 years. Smoke from the fires mixed with sunlight and hot dry air to form a cloud of smog. This pollution quickly spread and within days it was hanging over neighbouring countries including Malaysia, Singapore and Thailand. When the smoke combined with pollution from factories and cars, it soon became poisonous (有毒的). Dangerous amounts of CO became trapped under the smog and pollution levels rose. People wheezed (喘息) and coughed as they left the house and their eyes watered immediately. The smog made it impossible to see across streets and whole cities disappeared as grey soot (烟灰) covered everything. In some areas, water was hosed (用胶管浇) from high-rise city buildings to try and break up the smog. Finally, heavy rains, which came in November, put out the fires and cleared the air. But the environmental costs and health problems will remain. Many people from South-Eastern Asian cities already suffer from breathing huge amounts of car exhaust fumes (汽车排放的废气) and factory pollution. Breathing problems could well increase and many non-sufferers may have difficulties for the first time. Wildlife has suffered too. In lowland forests, elephants, deer, and tigers have been driven out of their homes by smog. But smog is not just an Asian problem. In fact, the word was first used in London in 1905 to describe the mixture of smoke and thick fog. Fog often hung over the capital. Sometimes the smog was so thick and poisonous that people were killed by breathing problems or in accidents. About 4,000 Londoners died within five days as a result of thick smog in 1952.

单选题He is {{U}}certain{{/U}} that the dictionary is just what I want.

单选题Graphene"s Superstrength Big technology comes in tiny packages. New cell phones and personal computers get smaller every year, which means these electronics require even smaller components on the inside. Engineers are looking for creative ways to build these components, and they"ve turned their eyes to graphene, a superthin material, made of carbon, that could change the future of electronics. This year"s Nobel Prize for Physics has been awarded to Andre Geim and Kostya Novoselov from the University of Manchester, UK. for the discovery of graphene. Graphene isn"t just small, it"s "the thinnest possible material in this world," says Novoselov. He calls it a "wonder material." It"s so thin that you would need to stack about 25,000 sheets just to make a pile as thick as a piece of ordinary white paper. If you were to hold a sheet of graphene in your fingers, you"d have no idea because you wouldn"t be able to see it. Carbon is one of the most abundant elements in the universe. Every known kind of life contains carbon. Graphene is a sheet of carbon, but only one atom thick. You don"t have to look far to find graphene—it"s all around you. If you want this high-tech wonderstuff, all you need is a pencil, paper and a little adhesive tape. Use the pencil to shade a small area on the paper, and then apply a small piece of adhesive tape over the area. When you pull up the tape, you"ll see that it pulls up a thin layer of some of the shading from your pencil. That layer is called graphite, one of the softest minerals in the world. Now stick the same piece of tape on another sheet of paper and pull the tape up—there should be an even thinner layer, this time left on the paper. Now imagine that you do this over and over, until you get the thinnest possible layer of material on the paper. This layer would be only one atom thick, and you wouldn"t be able to see it. Graphite is made of layers of graphene, so when you get to the thinnest possible layer, you"ve found graphene.

单选题She stood there, trembling with fear.

单选题Since the Uadvent/U of the motor car, road accidents have increased dramatically.

单选题You need feedback to monitor progress.

单选题Since ancient times people have found various ways to preserve meat.

单选题Her faith upheld her in times of sadness.

单选题It was advisable for you not to mention that.

单选题The Northern Lights The sun is stormy and has its own kind of weather. It is so hot and active that even the Sun"s gravity cannot hold its atmosphere in check! Energy flows away from the Sun toward the Earth in a stream of electrified particles that move at speeds around a million miles per hour. These particles are called plasma (等离子体), and the stream of plasma coming from the Sun is called the solar wind. The more active the Sun, the stronger the solar wind. The solar wind constantly streams toward the Earth, but don"t worry because a protective magnetic field surrounds our planet. The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles. The charged particles become trapped in magnetic belts around the Earth. When a large blast of solar wind crashes into the Earth"s magnetic field, the magnetic field first gets squeezed and then the magnetic field lines break and reconnect. The breaking and reconnecting of the magnetic field lines can cause atomic particles called electrons trapped in the belts to fall into the Earth"s atmosphere at the poles. As the electrons fall to the Earth, they collide with gas molecules in the atmosphere, creating flashes of light in the sky. Each atmospheric gas glows a different color. Oxygen and nitrogen glows red and green and nitrogen glows violet purple. As these various colors glow and dance in the night sky, they create the Northern Lights and the Southern Lights. Watching auroras (北极光) is fun and exciting, but normally you can only see them in places far north like Alaska and Canada. The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate (跳动), flicker (闪烁), or even move like waves. During solar maximum, 5 auroras are seen as far south as Florida, even Mexico! Auroras often seem to be very close to the ground, but the lowest aurora is still about 100 kilometers above the ground, a distance much higher than clouds are formed or airplanes can fly. A typical aurora band can be thousands of kilometers long, a few hundred kilometers high, but only a few hundred meters thick. We hope you are able to travel to far north places like the Arctic Circle and see the Northern Lights at least once during your lifetime. We know you will never forget it!

单选题He was persuaded to give up the idea.

单选题Sitting in the Land Rover with lions all around, the men felt very Uvulnerable/U.

单选题The manager allocates duties to the clerks. A. assigns B. persuades C. asks D. orders

单选题Shelly had prepared carefully for her biology examination so that she could be sure of passing it on her first endeavor.A. intentionB. attemptC. purposeD. desire

单选题Over thirty cities around the world boast more than five million {{U}}residents.{{/U}}