单选题Microcomputer proves itself more and more important in the business, so additional machines are {{U}}purchased{{/U}}.

单选题Compound microscopes have two separate lenses or sets of lenses.

单选题About one quarter of the workers in the country are employed in factories.

单选题I can hardly believe it, it's Uamazing/U.

单选题He maintained that the opinion was wrong.A. emphasizedB. repairedC. heldD. helped

单选题None of the five people killed by inhalational anthrax had been vaccinated against influenza.

单选题The researchers have just completed a study of driving situations.

单选题 Late-Night Drinking Coffee lovers beware. Having a quick "pick-me-up" cup of coffee late in the day will play havoc with your sleep. As well as being a stimulant, caffeine interrupts the flow of melatonin, the brain hormone that sends people into a sleep. Melatonin levels normally start to rise about two hours before bedtime. Levels then peak between 2 a.m. and 4 a.m., before falling again. "It's the neurohormone that controls our sleep and tells our body when to sleep and when to wake," says Manrice Ohayon of the Stanford Sleep Epidemiology Research Center at Stanford University in California. But researchers in Israel have found that caffeinated coffee halves the body's levels of this sleep hormone. Lotan Shilo and a team at the Sapir Medical Center in Tel Aviv University found that six volunteers slept less well after a cup of caffeinated coffee than after drinking the same amount of decal. On average, subjects slept 336 minutes per night after drinking caffeinated coffee, compared with 415 minutes after decal. They also took half an hour to drop off—twice as long as usual—and jigged around in twice as much. In the second phase of the experiment, the researchers woke the volunteers every three hours and asked them to give a urine sample. Shilo measured concentrations of a breakdown product of melatonin. The results suggest that melatonin concentrations in caffeine drinkers were half those in decal drinkers. In a paper accepted for publication in Sleep Medicine, the researchers suggest that caffeine blocks production of the enzyme that drives melatonin production. Because it can take many hours to eliminate caffeine from the body, Ohayon recommends that coffee lovers switch to decal after lunch.

单选题He picked a textbook from the bookshelf and then {{U}}commenced{{/U}} to read.

单选题As they move, glaciers push piles of rocks ahead of them.

单选题John is crazy about pop music.A. madB. sorryC. concernedD. worried

单选题When a great deal of word processing is carried out, standard letters and documents can be stored at once.A. brokenB. outdatedC. carried backD. performed

单选题Lower taxes would spur investment and help economic growth.

单选题Kan was {{U}}abducted{{/U}} because he was the only witness.

单选题Mother Nature Shows Her Strength Tornadoes and heavy thunderstorms moved across the Great Lakes and into Trumbull County on Saturday evening. The storms were dramatic and dangerous. George Snyder was driving the fire truck down Route 88 when he first noticed that a funnel cloud was behind him. "I stopped the truck and watched the funnel cloud. It was about 100 feet off the ground and I saw it go up and down for a while. It was moving toward Bradley Road and then suddenly it disappeared." Snyder said. Snyder only saw one of the funnel clouds that passed through northeastern Ohio on Saturday. In Trumbull County, a tornado turned trees onto their sides. Some trees fell onto houses and cars. Other trees fell into telephone and electrical wires as they went down. Amanda Symcheck was having a party when the storm began. "Knew something was wrong," she said. "I saw the sky go green and pink. Then it sounded like a train rushing toward the house. I started crying and told everyone to go to the basement for protection." The tornado caused a lot of damage to cars and houses in the area. It will take a long time and much money to repair everything. There was also serious water damage from the thunderstorms. The heavy rains and high wind caused the power to go out in many homes. The storms caused serious flooding in areas near the river. More than four inches of rain fell in parts of Trumbull County. The river was so high that the water ran into streets and houses. Many streets had to be closed to cars and trucks because of the high water. This made it difficult for fire trucks, police cars and other rescue vehicles to help people who were in trouble. Many people who live near the river had to leave their homes for their own safety. Some people reported five feet of water in their homes. Local and state officials opened emergency shelters for the people who were evacuated. The Red Cross served meals to them. "This was a really intense storm," said Snyder. "People were afraid. Mother nature can be fierce. We were lucky this time. No one was killed."

单选题Very often bacteria or viruses inhabit the body without causing illness, a condition known as the "carrier state".

单选题The （odd ）thing was that he didn't recognize me.

单选题Grouping stars by constellations is a handy way of mapping the sky.

单选题Our lives are intimately bound up with theirs.

单选题Ammonia, one of the earliest known nitrogen compounds,was originally produced by distilling organic materials.