请先阅读下面的短文，掌握其大意．然后在每小题所给的A，B，C，D四个选项中，选出可以填入空白处的最佳选项。
Today some people call Amsterdam the "City of Bicycles" because it is a city which is flat and convenient（方便）for bicycles.
In the 1960s, a group of cycling fans1an idea . They believed that it would be better for everybody if only bicycles were allowed in the city centre. They were2that this would help to save energy, reduce pollution and provide free public transport. The group painted hundreds of bicycles3and placed them in public places around Amsterdam for people to use.4was allowed to take them and use them for short journeys, whether he was a local or a foreigner, Wherever someone finished a journey, they would5the bike there for someone else to use. The problem was that it didn't work-thieves took all the bicycles6 weeks!
7,more than thirty years later, the "white bike" is back in town-this time with a computer chip(芯片)to8 its every move! To take a bicycle, you have to put a special card inside. The new "White bike" is not white any more but is an unusual9with bright colours. The bikes are parked at special parking places and people who want to use them have to take them to another place that has enough room.
There is already less traffic in central Amsterdam, 10 both locals and tourists have been using the white bikes. Thanks to the good ideas of lots of people, like the cycling fans in the 1960s, many people around the world have been enjoying city centre streets without cars for many years.
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