13．In its early history，Chicago had floods frequently，especially in the spring，making the streets so muddy that people，horses，and carts got stuck．An old joke that was popular at the time went something like this：A man is stuck up to his waist in a muddy Chicago street．Asked if he needs help，he replies，"No，thanks．I've got a good horse under me．"
The city planner decided to build an underground drainage （排水） system，but there simply wasn't enough difference between the height of the ground level and the water level．The only two options were to lower the Chicago River or raise the city．
An engineer named Ellis Chesbrough convinced the city that it had no choice but to build the pipes above ground and then cover them with dirt．This raised the level of the city's streets by as much as 12 feet．
This of course created a new problem：dirt practically buried the first floors of every building in Chicago．Building owners were faced with a choice：either change the first floors of their buildings into basements，and the second stories into main floors，or hoist the entire buildings to meet the new street level．Small wood-frame buildings could be lifted fairly easily．But what about large，heavy structures like Tremont Hotel，which was a six-story brick building？
That's where George Pullman came in．He had developed some house-moving skills successfully．To lift a big structure like the Tremont Hotel，Pullman would place thousands of jackscrews （螺旋千斤顶） beneath the building's foundation．One man was assigned to operate each section of roughly 10 jackscrews．At Pullman's signal each man turned his jackscrew the same amount at the same time，thereby raising the building slowly and evenly．Astonishingly，the Tremont Hotel stay open during the entire operation，and many of its guests didn't even notice anything was happening．Some people like to say that every problem has a solution．But in Chicago's early history，every engineering solution seemed to create a new problem．Now that Chicago's waste water was draining efficiently into the Chicago River，the ci ty's next step was to clean the polluted river．
29．The author mentions the joke to showB．
A．horses were fairly useful in Chicago
B．Chicago's streets were extremely muddy
C．Chicago was very dangerous in the spring
D．the Chicago people were particularly humorous
30．The city planners were convinced by Ellis Chesbrough toD．
A．get rid of the street dirt
B．lower the Chicago River
C．fight against heavy floods
D．build the pipes above ground
31．What can we conclude about the moving operation of the Tremont Hotel？A
A．It went on smoothly as intended．
B．It interrupted the business of the hotel．
C．It involved Pullman turning ten jackscrews．
D．It separated the building from its foundation．
分析 本文属于说明文阅读，作者通过这篇文章主要向我们描述了芝加哥城的问题和改造方案，他们因为洪水的经常泛滥导致大街上总是泥泞不堪，但也已经出台了各种应对政策．
解答 29．B．细节推理题．根据文章的第一段第一句话：In early history，Chicago had floors frequently，especially in the spring，making the streets so muddy that people，horses，and carts got stuck．可知芝加哥因为洪水的经常泛滥导致大街上总是泥泞不堪，行人，马和车全部都堵在路上．所以作者提及那个玩笑是为了突出芝加哥这一特点，故选B．
30．D．细节理解题．根据第三段第一句话：An engineer named Eill Chesbrough convinced the city that it had no choice but to build the pipes above ground and then cover thenwith dirt．可知以Eill Chesbrough为首的人们认为应该在地上埋下排水管道，故选D．
31．A．细节推理题．根据倒数第二段中的倒数第二句话：At Pullman's signal each man turned his jackscrew the same amount at the same time，thereby raising the building slowly and evenly．（在Pullman的指导下，每个人同时抬起他们手中的千斤顶，因此建筑就被慢慢地、平整地抬起来了）可知A项正确，故选A．
点评 考察学生的细节理解和推理判断能力，做细节理解题时一定要找到文章中的原句，和题干进行比较，再做出正确的选择．在做推理判断题不要以个人的主观想象代替文章的事实，要根据文章事实进行合乎逻辑的推理判断．
