完形填空

　　When my wife, who is Spanish, spent her first winter in London a few years ago, she used to ask me time and again：“Where’s the fog?”Almost all foreigners 　　1　　 to find the city full of yellow – grey fog for most of the years．Dickens, who was 　　2　　 responsible for painting this 　　3　　 in people’s minds, certainly wasn’t joking in those days．In the nineteenth century people used to say 　　4　　 someone attempted to kill himself by 　　5　　 into the Thames, he would be choked by the fog and poisoned by the terrible 　　6　　 of the river before he had time to drown himself．In fact, the situation has 　　7　　 only in recent years．When I was a boy in London thirty years ago, I was often unable to see 　　8　　 of the road when I left home on winter mornings．

　　The key steps that have turned London into one of the 　　9　　 cities in the world were 　　10　　 at the end of the 1950s．But Londoners still find it 　　11　　 that fog hardly returns．Actually the 　　12　　 took place as a result of two main improvements．Factories were forced to fix equipment for air cleaning 　　13　　 close down, and local people were not allowed to 　　14　　 coal unless it was smoke – free．But the 　　15　　 incredible miracle in London occurred 　　16　　 1964 when the Thames Water Authority began to pump vast 　　17　　 of dissolved oxygen into the river．　　18　　, varieties of fish that had gradually disappeared from the Thames since 1800 have 　　19　　, and some are 　　20　　 caught by fishermen outside the House of Parliament(议会)．

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