单选题Photojournalist Margaret Bourke-White became famous for her {{U}}coverage{{/U}} of significant events during the Second World War.

单选题Dumped waste might Ucontaminate/U water supplies.

单选题Hurricane (飓风) Katrina A．hurricane is a fiercely powerful, rotating (旋转的) form of tropical storm that can be 124 to 1, 240 miles in diameter. The term hurricane is derived from Hurican, the name of a native American storm god. Hurricanes are typical of a calm central region of low pressure between 12 to 60 miles in diameter, known as the eye. They occur in tropical regions. Over its lifetime, one of these storms can release as much energy as 10,000 nuclear bombs. The seed for hurricane formation is a cluster (聚焦) of thunderstorms over warm tropical waters. Hurricanes can only form and be fed when the sea-surface temperature exceeds 27℃ and the surrounding atmosphere is calm. These requirements are met between June and November in the northern part of the world. Under these conditions, large quantities of water evaporate (蒸发) and condense (冷凝) into clouds and rain-releasing heat in the process. It is this heat energy, combined with the rotation of the Earth, that drives a hurricane. When the warm column of air from the sea surface first begins to rise, it causes an area of low pressure. This in turn creates wind as air is drawn into the area. This spinning wind drags up more moist air from the sea surface in a process that strengthens the storm. Cold air falls back to the ocean surface through the eye and on the outside of the storm. Initially, when wind speeds reach 23 miles per hour, these mild, wet and grey weather systems are known as depressions, or low air pressure. Hurricane Katrina formed in this way over the south-eastern Bahamas on 23 August 2005. Katrina has had a devastating impact on the Gulf Coast of the US, leaving a disaster zone of 90,000 square miles in its wake (尾迹)—almost the size of the UK. Thousands have been killed or injured and more than half a million people have become homeless in a humanitarian (人道主义的) crisis of a scale not seen in the US since the Great Depression. The cost of the damage may top $100 billion.

单选题Most animal fats are saturated, containing more hydrogen than carbon, and do not spoil as easily as unsaturated fats.

单选题This kind of material was seldom used in building houses during the middle ages.

单选题The young man was accused of theft in the supermarket.A. arrested forB. charged withC. praised forD. described as

单选题You should cultivate the habit of reading carefully.

单选题The ground on which the church stands has always been regarded as Usacred/U.

单选题From my {{U}}standpoint{{/U}}, you know, this thing is just funny. A.position B.point of view C.knowledge D.opinion

单选题Weaving with Light In the Sierra Madre mountain range of west central Mexico, the native Huichol people live much the way their ancestors did—without electricity. That"s because it"s too expensive to string power lines to the remote mountain areas where they live. To help support themselves, the Huichol create beautiful artwork. They sell their art in cities hundreds of miles away from their villages. And without electricity—at home or on the road, they can only Work during daylight hours. When it gets dark, they must stop whatever they"re doing. Now, a team of scientists, designers, and architects is using new technologies to provide the Huichol with light after the sun sets. The scientists" technique involves weaving tiny electronic crystals into fabrics that can be made into clothes, bags, or other items. By collecting the sun"s energy during the day, these lightweight fabrics provide bright white light at night. Their inventors have named the fabrics "Portable Lights." Portable Lights have the potential to transform the lives of people without electricity around the world, says project leader Sheila Kennedy. "Our invention," Kennedy says, "came from seeing how we could transform technology we saw every day in the United States and move it into new markets for people who didn"t have a lot of money." At the core of Portable Light technology are devices called high-brightness light-emitting diodes, or HB LEDs. These tiny lights appear in digital clocks, televisions, and streetlights. LEDs are completely different from the light bulbs. Most of those glass bulbs belong to a type called incandescent lights. Inside, electricity heats a metal coil to about 2,200 degrees Celsius. At that temperature, bulbs give off light we can see. Ninety percent of energy produced by incandescent lights, however, is heat—and invisible. With all that wasted energy, bulbs burn out quickly. They are also easily broken. LEDs, on the other hand, are like tiny pieces of rock made up of molecules that are arranged in a crystal structure. When an electric current passes through an LED, the crystal structure produces light. Unlike incandescent bulbs, they can produce light of various colors. Within an LED, the type of molecules and their particular arrangement determines what color is produced.

单选题George Washington Carver was esteemed for his contributions in the fields of botany and chemistry.

单选题New secretaries came and went with Umonotonous/U regularity.

单选题There are only five minutes left, but the outcome of the match is still in doubt.

单选题Citizen Scientists Understanding how nature responds to climate change will require monitoring key life cycle event-flowering, the appearance of leaves, the first frog calls of the spring all around the world. But ecologists can't be everywhere so they're turning to non-scientists, sometimes called citizen scientists, for help. Climate scientists are not present everywhere. Because there are so many places in the world and not enough scientists to observe all of them, they're asking for your help in observing signs of climate change across the world. The citizen scientist movement encourages ordinary people too observe a very specific research interest--birds, trees, flowers budding, etc. and send their observations to a giant database to be observed by professional scientists. This helps a small number of scientists track a large amount of data that they would never be able to gather on their own. Much like citizen journalists helping large publications cover a hyper-local beat, citizen scientists are ready for the conditions where they live. All that's needed to become one is a few minutes each day or each week to gather data and send it in. A group of scientists and educators launched an organization last year called the National Phenology Network. "Phenology" is what scientists call the study of the timing of events in nature. One of the group's first efforts relies on scientists and non-scientists alike to collect data about plant flowering and leafing every year. The program, called Project BudBurst, collects life cycle data on a variety of common plants from across the United States. People participating in the project which is open to everyone record their observations on the Project BudBurst website. "People don't have to be plant experts, they just have to look around and see what's in their neighborhood," says Jennifer Schwartz, an education consultant with the project. "As we collect this data, we'll be able to make an estimate of how plants and communities of plants and animals will respond as the climate changes./

单选题Jean has made up her mind not to go to the meeting.

单选题Floods have undermined the foundation of the ancient bridge.A. destroyedB. reachedC. broadenD. covered

单选题Academic records cannot be duplicated. A. borrowed B. purchased C. copied D. rewritten

单选题His marked personality changes were {{U}}brought about{{/U}} by a series of unfortunate events.

单选题One of the reasons why business or government has not taken tough measures to stop hacking is that

单选题Remember back in 2001 when BP went" Beyond Petroleum"? It was a brilliant marketing campaign, but it had less to do with changing the company's business model than positioning Lord John Browne as the Teflon oil executive. All but a tiny fraction of BP's revenue came, and still comes from oil. So how should we take the spate of new green announcements from the world's major oil firms? In July, ExxonMobil announced big plans to grow green algae to fuel cars; last week, Chevron unveiled the world's largest carbon-sequestration project in Australia; and in recent months, Valero, Marathon, and Sunoco carried out a series of acquisitions that resulted in Big Oil controlling 7 percent of the U. S. ethanol business. Who was John Browne?A. The Teflon oil executive.B. The executive of Chevron.C. The executive of ExxonMobil.D. The executive of Big Oil.