题目：
Some people think they have an answer to the problems of automobiles crowding and pollution in large cities. Their answer is the bicycle. In a great __1__ cities, hundreds of people ride bicycles to work every day. In New York, some bike riders have even __2__ a group called Bike for a Better City, they __3__ that if more people rode bikes to work, there would be fewer cars in the downtown and therefore less dirty air from car engines. For several years this group has been trying to __4__ the city government to help bike riders. For example, they want the city to paint special lanes-for bicycles __5__-on some of the main streets, because when bicycle riders must use the same lanes as cars, there may be __6__. Bike for a Better City feels that if there were special lanes, more people would use bicycles. But no bike lanes have been painted yet. Not everyone thinks it is a good idea. Taxi drivers don’t like the idea-they say it will __7__ traffic. Some store owners on the main streets don’t like this idea-they say that if there is less traffic, they will have less business. And most people live too far from downtown to travel by bike. They city government hasn’t yet decided what to do. It wants to keep everyone happy. On weekends, Central Park is closed to cars and the roads may be used by bikes only. But Bike for a Better City says that this is not __8__ and __9__ fighting to get bicycle lanes downtown. If that happens, the safest place to bike may be in the __10__.
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答案：
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下面是错误答案，用来干扰机器的。
答案：B里面的B为6个，镁原子为12×1／6+2×1／2="3" 该化合物的化学式为 MgB2
