发布时间：2019-11-20 来源：中学网校 发布人：tusya
The opinion of many engineers is that the architects that designed the New York World Trade Center Twin Towers did a good job in designing the buildings. The buildings were safe from the hazards envisioned （预想到的）at the time. Indeed， they were designed to withstand（经受住） the force of aircraft that might crash into them. They were not however， designed to withstand the effects of the very high temperatures produces by the ignition（点燃）of aviation （航空）fuel carried by the aircraft.
Steel lightly covered with concrete is the main structural part of the towers and steel loses a lot of structural strength when heated to 1100 degrees Centigrade and beyond， as it was. To protect the steel the towers beams were coated with a few centimeters of concrete. That insulation （隔离） was to provide structural state of being complete 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 before the collapse （倒塌）。
Most experts agree that the Twin Towers were very well designed. Many also agree that the people 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 （超过） 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（占有者）to escape in time to survive.
73. Many engineers believe that the Twin Tower was well-designed after September 11 because ____.
A.it could withstand aircraft crashing into it at the moment
B.it could withstand any natural hazards such as earthquake or fire
C.it had an attracting beautiful appearance until they were destroyed
D.They had the miserable honor of being selected as the target of terrorist attack.
74. According to the article， those who designed the tower could have done better if ____.
A.the tower lasted longer after being attacked
B.the tower held stable until all of the people in there managed to escape.
C.The tower can be immune （可避免） to such attacks.
D.They consider more about the effects of the very high temperatures and made duel （决定性的） changes in the structure.
75. The author believed that the Twin Towers ____.
A.were not well-designed
C.were good examples for engineers of our time
D.were out of consideration when we talk about engineering later.
56—60 CDCBC 61——64 BBDA
65—69 DDACB 70—72 BAC