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Many people have cars in the city．But pollution is a problem because of the （51） ______ ．Nowadays some downtown （市中心） areas around the world don’t have cars．These car-free zones （无车区） are （52） ______ for people，bicycles，and public transportation only．
Eight million people （53） ______ in the center of London and another two million people go to work there every day．The downtown area is very（54） ______ with hundreds of cars，buses，and taxis，but there are （55） ______ a lot of beautiful parks with free music concert．At lunchtime，many people go there for a rest （56） ______ they get off work．
Parts of Tokyo are always crowded with hundreds of people-but no cars!These modern car-free zones are （57） ______ popular and people like shopping there．
In the past，Bogota was polluted because there （58） ______ lots of cars and traffic．Now the downtown area is car-free zone and the air is （59） ______ !Many people don’t have a car and half a million people take the bus （60） ______ ．There are lots of stores．It’s not expensive．