单项选择题

案例分析题

A scientific discovery is often made 【C1】______before someone is able to put it to use.【C2】______，scientists discovered how to split atoms decades 【C3】______the invention of the atomic bomb and the use of 【C4】______power to produce electricity.But sometimes discovery and 【C5】______happen at the same time，as occurred more than thirty years ago 【C6】______the discovery of coherent light and the invention of the laser.
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】（）