单选题
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
【正确答案】
B
【答案解析】
[精解] 文中提到激光的强度是在第二段的末尾：The light in a laser beam，however， is concentrated．．．．
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