UNDER THE CITY STREETS While skyscraper offices and elegant apartment blocks remain the public face of most major cities, these cities also have a mass of secret tunnels and hidden pipes below 【B1】______ which keep everything working. This other world exists beneath many of our greatest cities, forgotten or neglected by all but a tiny 【B2】______ of engineers and historians. For example, there are more than 150 kilometres of rivers under the streets of London. Most have been 【B3】______ over and, sadly, all that 【B4】______ is their names. Perhaps the greatest 【B5】______ to the city is the River Fleet, a 【B6】______ great river which previously had beautiful houses on its 【B7】______ It now goes underground in the north of the city and 【B8】______ into the River Thames by Blackfriars Bridge. The London Underground 【B9】______ 1000 kilometres of underground railway track winding under the capital and more than 100 stations below street level. Along some underground railway 【B10】______ commuters can sometimes catch a 【B11】______ glimpse of the platforms of more than forty closed stations which have been left under the city. 【B12】______ some are used as film sets, most【B13】______ forgotten. Some have had their entrances on the street turned into restaurants and shops, but most entrances have been 【B14】______ down. Interestingly, there is also a special underground Post Office railway that 【B15】______ a link between east and west London postal centres.【B1】______A．landB．groundC．soilD．earth