Ever since the first skyscraper(摩天大楼) was built in Chicago in 1883, more and more building

Ever since the first skyscraper(摩天大楼) was built in Chicago in 1883, more and more buildings that reach for the skies have been constructed in the large cities of the world.
For many years, the Empire State Building in New York City was the tallest building in the world. It was 1250 feet high when it was opened in 1931. Then in 1951 a TV transmission⑨ tower was added for radio and television broadcasts. This tower added 222 feet to its height.
Soon other skyscrapers were built. The World Trade Center in New York, 1350 feet high, and Chicago’s Sears Tower, 1450 feet high. No one can say how much higher skyscrapers will go in the future.
Early skyscrapers were built with thick heavy walls of solid brick, stone, or concrete. Now the new skyscrapers are built with a steel framework⑩ that supports the weight of the building. The solid walls are no longer needed, and the framework makes it possible to build to greater heights.
Built at first mainly for offices and shops, some skyscrapers are now becoming homes for people who want to live in the center of the city. The 100-story John Hancock Center, a Chicago skyscraper that opened in 1970, is an example. Between the first and 43rd floor, there are offices and shops. There is a swimming pool on the 44th floor. From the 45th floor to the 92nd there are apartments. The people who live in these apartments can look down on the clouds instead of up at them.
67.What happened to the Empire State Building in 1951?
A. It was no longer the tallest building in the world.
B. A tower was added to it, which increased its height.
C. It was transformed into a radio and television broadcasting station.
D. It provided homes for people who wanted to live in the city center.
68.We cannot know how much taller skyscrapers will become in the future because .
A. a TV transmission tower can be added
B. solid walls of brick, stone or concrete are no longer needed
C. the steel framework makes it possible to build to greater heights
D. some skyscrapers are now becoming homes
69.Originally, skyscrapers were built as .
A. business centers and offices
B. radio and television broadcasting stations
C. apartment complexes
D. apartment and shops
70.How do people benefit from living in the John Hancock Center?
A. They can enjoy looking at the clouds above the building.
B. They have all the city center facilities nearby.
C. They can use the swimming pool on the top of the building.
D. They can work at offices inside the building.B

(答案→)B 解析：

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