题目内容
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A.words
B.phrases
C.objectives
D.clauses
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The word laser 【C7】______ "light amplification by stimulated emission of radiation." To many people, lasers are very mysterious, but a laser is simply a 【C8】______ that produces a strong light. The light from the laser is called 【C9】______ light because it is light that only moves in one direction. 【C10】______ , incoherent light, like the light from the sun or light from a bulb, moves away from its source 【C11】______ all directions, so its strength is very spread out. The light from a laser, moving in only one direction and 【C12】______ in a narrow beam, is much stronger. Laser light is created by a 【C13】______ called stimulated emission. In this process, the atoms of a certain substance, such as a crystal or a gas, are excited 【C14】______ that they produce coherent light. A person working with a laser can aim this coherent light, 【C15】______ a laser beam, in any direction.
As soon as the laser was developed, scientists began thinking of practical applications 【C16】______ it. One of the earliest uses was to make extremely precise measurements of distance and speed. 【C17】______ , the distance to the moon was measured to within a foot, and the speed of light was measured to 【C18】______ a thousandth of a mile per second. As time 【C19】______ , many more applications for the laser were 【C20】______ .
【C1】
A．long
B．early
C．very
D．earlier
The desired level is one that seems slightly greater than that normally heard in conversation. If the room is large and filled with people, you will have to put an appropriate amount of power in your voice to be easily heard. In some cases, you may require electronic amplification, which will usually enable you to speak in an ordinary conversational tone.
Furnishings such as heavy carpets and drapes absorb a good deal of sound, thereby creating a deadening effect on the speaker's voice. You should be able to judge the effects of the furnishings after speaking the first few sentences. You can then modify your voice level as necessary to account for any sound-absorbing material.
The ambient noise in the room may be made up of motor sounds from and overhead projector, air-conditioning, outside traffic, etc. You may find it necessary to vary your voice level at times to adjust for changes in the ambient noise level.
Finally, you should be aware of cues from members of the audience who may communicate by body language an inability to hear what you are saying.
According to the text, what is the easiest distractions to eliminate？
A．The size of the room.
B．The topic engaged in.
C．The audience.
D．Too soft voice.
Albert Einstein was the first to suggest the existence of stimulated emission in a paper published in 1917. However, for many years physicists thought that atoms and molecules always were much more likely to emit light spontaneously and that stimulated emission thus always would be much weaker. It was not until after the Second World War that physicists began trying to make stimulated emission dominate. They sought ways by which one atom or molecule could stimulate many others to emit light, amplifying it to much higher powers.
The first to succeed was Charles H. Townes, then at Columbia University in New York. Instead of working with light, however, he worked with microwaves, which have a much longer wavelength, and built a device he called a "maser", for Microwave Amplification by the Stimulated Emission of Radiation. Although he thought of the key idea in 1951, the first maser was not completed until a couple of years later. Before long, many other physicists were building masers and trying to discover how to produce stimulated emission at even shorter wavelengths.
The key concepts emerged about 1957. Townes and Arthur Schawlow, at Bell Telephone Laboratories, wrote a long paper outlining the conditions needed to amplify stimulated emission of visible light waves. At about the same time, similar ideas crystallized in the mind of Gordon Gould, then a 37-year-old graduate student at Columbia, who wrote them down in a series of notebooks. Townes and Schawlow published their ideas in a scientific journal, Physical Review Letter, but Gould fried a patent application. Three decades later, people still argue about who deserves the credit for the concept of the laser.
The word "intervention" (Line 3, Para. 1) can best be replaced by ______.
A．need
B．device
C．influence
D．reproduction
试区分基因扩增(gene amplmcation)和翻译扩增(translational amplification)。
Some conductors ______ sound amplification at their concerts.
A．let
B．allow
C．proscribe
D．permit
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