The laser beam is very strong because（）

The reason why the laser beam is very strong is that ______.

A．it is artificially illuminated (照亮)

B．it is made up of a concentrated beam of light

C．it sends out heat in all directions

D．its heat is increased by the heat of the sun

The reason why the laser beam is very strong is that ______.

A．it is artificially illuminated

B．it is made up of a concentrated beam of light

C．it sends out heat in all directions

D．its heat is increased by the heat of the sun

The reason why the laser beam is very strong is that

A．it is artificially illuminated

B．it is made up of a concentrated beam of light

C．it sends out heat in all directions

D．its heat is increased by the heat of the sun

The laser beam is so strong because ______.

A．it is a highly intensified beam of light

B．its strength is increased by the heat of the sun

C．it can be connected to strong light sources

D．it is a concentration of light from different sources

The laser beam is so strong because ______.

A．it is composed of a concentrated beam of light

B．its heat is increased by the heat of the sun

C．it can be plugged into an ordinary light fitting

D．it sends out heat in many different directions

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A.it is artificially illuminated

B.it is made up of a concentrated beam of light

C.it sends out heat in all directions

D.its heat is increased by the heat of the sun

A laser beam can be turned into a ______ weapon.

A．dead

B．deathly

C．dying

D．deadly

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】

A．long

B．early

C．very

D．earlier

uces a very strong light.