Câu hỏi:

Read the article about endangered species. For questions 1-10, choose the correct answer A, B, C or D.     

      The word laser was coined as an acronym for Light Amplification by the Stimulated Emission of Radiation. Ordinary light, from the Sun or a light bulb, is emitted spontaneously, when atoms or molecules get rid of excess energy by themselves, with out any outside intervention. Stimulated emission is different because it occurs when an atom or molecule holding onto excess energy has been stimulates to emit it as light          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 stimulates 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 stomp 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 ha 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 complete 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 shorted wavelengths.          The key concepts emerged about 1957. Townes and Arthur Schawlow, then 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 if Gordon Gould, then a 37-years-old graduate student at Columbia, who wrote them down in a series of notebook. Townes and Schawlow published their ideas in a scientific journal, Physical Review Letters, but Gould files a patent application. Three decades later, people still argue about who deserved the credit for the concept of the laser.

The word “coined” in line I could best be replaced by _________