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  3. The opinion of many engineers is that the architects that designed tine New York World Trade Center Twin Towers did a good job i

The opinion of many engineers is that the architects that designed tine New York World Trade Center Twin Towers did a good job i

admin2012-12-13  56
问题     The opinion of many engineers is that the architects that designed tine New York World Trade Center Twin Towers did a good job in designing the buildings. The buildings were safe from the hazards envisioned at the time. Indeed, they were designed to withstand the force of aircraft that might crash into them. They were not, however, designed to withstand the effects of the very high temperatures generated by the ignition of tons of aviation fuel carried by the aircraft.
    Steel lightly covered with concrete is the main structural component of the towers and steel loses a lot of structural strength when heated to 1,100 degrees Centigrade and beyond, as it was. To shield the steel the towers beams(柱梁) were c0ated with a few centimeters of concrete. That insulation was to provide structural integrity for at least 1 hour of fire. The towers met that test. The south tower lasted 62 minutes. The north, 103 minutes. Tragedy followed when not all could escape prior to the collapse.
    Most experts agree that the Twin Towers were very. well designed. Many also agree that the pan pie planning the attacks were very knowledgeable and aimed the aircraft at a height that would effect the most damage. The aircraft crash and the resulting fuel fed fires were aimed at about the 90th floor. That was just high enough to insure that the upper floors would weaken with the heat and crack down, dropping into the remaining part of the building.      The mass of the falling top floors created such a falling load that some experts estimate it exceeded by 5 to 10 times normal bearing loads. The effect was like a giant hammer, each floor contributing more weight to be born by the next floor down.
    Were the Trade Towers well designed? Engineers say yes. But, the public refers to the belief that architects will never again design a tall building without considering the effects of terrorist attacks of all potential kinds. That not only includes the ability of the structure to withstand attack but the means to allow the buildings occupants(居住者) to escape in time to survive.
The part of the building below 0th floor ______.
选项 A、remained where they were
B、cracked down because of the burning
C、was hammered down by the falling upper part
D、was safe after the attack
答案C
解析 解题关键是第三段第四句和第四段，第三段第三句话提到飞机与大厦相撞，燃料着火，火焰直指90层。而后作者在第四句说That was just high enough to insure that the upper floors would weaken with the heat and crack down，dropping into the remaining part of the building.，意思是“那一高度足以使上面的楼层因无法经受高温而倒塌，往下面的楼层坠落”；接着作者在第四段指出，上面楼层的倒塌给下面造成更大压力，造成巨锤效应，使大厦最终整体倒塌，这正是C)的含义。A)和D)与原文理解不符；B)中的burning过于笼统，故排除。
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