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  3. The very high temperatures attained in a nuclear explosion result in the formation of an extremely hot intense mass of gas calle

The very high temperatures attained in a nuclear explosion result in the formation of an extremely hot intense mass of gas calle

admin2013-03-11  41
问题     The very high temperatures attained in a nuclear explosion result in the formation of an extremely hot intense mass of gas called a fireball. For a l0-kiloton (千吨，核弹当量单位) explosion in the air, the fireball will attain a maximum diameter of about 300m; for a l0-megaton (兆吨，核弹当量单位) weapon the fireball may be 4.8 km across. A flash of heat radiation is emitted from the fireball and spreads out over a large area, but with steadily decreasing intensity. The amount of heat energy received a certain distance from the nuclear explosion depends on the power of the weapon and the state of the atmosphere. If the visibility is poor or the explosion takes place above clouds, the effectiveness of the heat flash is decreased. The heat radiation falling on exposed skin can cause what called flash burns. A 10-kiloton explosion in the air can produce moderate (second-degree) flash burns, which require some medical attention, as far as 2.4 km from ground zero; for a 10-megaton bomb, the corresponding distance would be more than 32 km. milder burns of bare skin would be experienced even farther out. Most ordinary clothing provides protection from the heat radiation, as does almost any opaque (不透明的) object. Flash burns occur only when the bare skin is directly exposed, or if the clothing is too thin to absorb the heat radiation.
    The heat radiation can start fires in dry, flammable materials, for example, paper and some fabrics, and such fires may spread if conditions are suitable. The evidence from the A-bomb explosions over Japan indicates that many fires, especially in the area near ground zero, originated from secondary causes, such as electrical short circuits, broken gas lines, and upset furnaces and boilers in industrial plants. The blast damage produced wreckage that helped to maintain the fires and denied access to fire-fighting equipment. Thus, much of the fire damage in Japan was a secondary effect to the blast wave.
    Under some conditions, such as existed at Hiroshima but not at Nagasaki, many individual fires can combine to produce a fire storm similar to those that accompany some large forest fires. The heat of the fire causes a strong updraft (向上排气), which produces strong winds drawn in toward the center of the burning area. These winds fan the flame and convert the area into a disaster in which everything flammable is destroyed.
The example of Hiroshima is given to______.
选项 A、give the readers a clear image of the explosion of atomic bombs
B、to show that the explosion of atomic bombs can lead to forest fires
C、to illustrate the secondary effect of the atomic bomb
D、to explain why the damages are different at Hiroshima and Nagasaki
答案C
解析 推理判断题。文章最后一段描写广岛原子弹爆炸后，零星的小火演变成了大火灾，而在上一段的结尾处已经讲到火灾通常是冲击波的二次破坏造成的。所以，此处广岛原子弹的爆炸事件是来说明冲击波二次破坏的威力。
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