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单选题 A dust explosion occurs when a large amount of dust mixed with air catches fire. Around paper mills, threshing machines, and com mines, enough dust gathers to make dust explosions a hazard, especially when there is a nearby source of heat. Most metals that do not ordinarily burn will catch fire when they are finely ground. Many substances that do not burn easily when in large pieces will explode quickly when in the form of ______
学科：工程学科英语
时间：2023-06-11 16:39:57
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题目1单选题
The shorter a pendulum is, the faster it swings. Most pendulum clocks have a setscrew by which one may adjust the length of the pendulum when the clock is not keeping accurate time. If the clock is running too fast, the pendulum is swing too fast and it should be ______A. lengthenedB. replacedC. shortenedD. stopped
题目2单选题
During the last half of the 19th century, the United States and Germany made rapid progress in industrialization. Their deposits of coal and iron — essential factors in developing industry — aided them in becoming ______A. self-sufficientB. manufacturing hubsC. democraciesD. cultural leaders
题目3单选题
Steel containing even less than one percent of molybdenum is remarkably hard and useful for making fine cutting tools. Many molybdenum ores that contain less than 1 percent by mass of molybdenum are mined because the metal is rare and ______A. valuableB. unavailableC. al alloyD. sharp
题目4单选题
A dust explosion occurs when a large amount of dust mixed with air catches fire. Around paper mills, threshing machines, and com mines, enough dust gathers to make dust explosions a hazard, especially when there is a nearby source of heat. Most metals that do not ordinarily burn will catch fire when they are finely ground. Many substances that do not burn easily when in large pieces will explode quickly when in the form of ______A. heatB. dustC. metalsD. coal
题目5单选题
Often, as soon as object is invented by one person, others quickly start making improvements and change in the object. Alexander Graham Bell invented the telephone, but so many changes have been made in it since it was invented that ______A. more people now can afford to have one in their homesB. we really cannot say that Bell invented itC. "telephone" is no longer a proper name for the instrumentD. one would scarcely recognize the original as being a telephone
题目6单选题
Iron is of prime importance in tool making, weaponry, transport facilities, construction, and machinery. Because of its unmatched magnetic properties, iron provides the cores that are used in all electric generators, and the production of electricity on any large scale would be impossible without it. Although gold, silver, and some other metals cost more and are also used in industry, iron is the most ______A. rareB. dispensableC. vitalD. expensive
题目7单选题
Disagreeable or too loud sounds can be so annoying to workers that their efficiency is reduced. Acoustical engineers have made many factories more pleasant to work in by the use of insulating materials that reduce noise. At the same time, the productivity of the workers is often ______A. musicalB. expensiveC. pleasantD. increased
题目8单选题
Many deep-sea divers are lowered and raised by a crew on the surface and receive their oxygen supply through tubes to the surface. Skin-divers use an independent system called scuba, self-contained underwater breathing apparatus. Open-circuit scuba equipment allows bubbles of air to come to the surface. Navy skin-divers use a closed or semi-closed circuit apparatus. With this type of apparatus, the enemy cannot detect the diver's presence because ______A. no bubbles escape to the surfaceB. the diver is down too deepC. there is not boat in sightD. the apparatus blends with the sea
题目9单选题
Acetylene, an invisible gas, produces a flame whose light penetrates fog and darkness remarkable well. This property, along with the capacity of the acetylene generator to operate without attention for long periods of time, makes the gas valuable for use in ______A. blowtorchesB. lighthousesC. industrial heatingD. welding
题目10单选题
In the port cities of London, Liverpool, and Le Havre, the water depth varies greatly between low tide and high tide, wet docks, or basins, have been built in these places. The walls of these concrete docks have gates that operate to maintain a navigable water level when ______A. dry docks are scarceB. the dock is crowdedC. no ships are nearD. the tide is low
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