单项选择题

Tourism is an essential part of Britain"s income. It employed about 1.4 million people and contributed about 3.5 percent to the GDP in the early 2000s. Visitors to Britain come from all over the world, with the largest number from the United States, followed by France, Germany, Ireland and Netherlands. They were attracted by Britain"s heritage and arts, historic buildings, monuments, museums and galleries. With over 27 million tourists a year, the United Kingdom is ranked as the sixth major tourist destination in the world.
The British Tourist Authority, which is supported by the government, promotes tourism in Britain and maintains hundreds of Tourist Information Centers to assist visitors. England, Scotland, Wales and Northern Ireland have their own government-supported tourist boards as well.
London, the most popular tourist destination, is crowded with tourists throughout the year. Among the sites regularly visited by millions are the Tower of London, the Houses of Parliament, Buckingham Palace and West Minister Abbey (修道院,大教堂). At night visitors enjoy the hundreds of theatres and pubs in London. Liverpool is a city in the metropolitan country of Merseyside (默西塞德郡) in northwest England—the second largest export of Britain, and it still possesses some manufacturing bases. Liverpool is world famous as the city where the Beatles came from. In Scotland, Edinburgh Castle looms over the capital. Great cathedrals from the Middle Ages still dominate the skylines of many English cities. In Wales, the remains of Tintern Abbey and the small but beautiful Saint David"s Cathedral (大教堂) are outstanding. There are a lot of stately homes in Britain. Among the more famous is Blenheim Palace, the home of the Churchill family. Hampton Court Palace, just outside of London, was one of the homes of Henry Ⅷ. The Palace of the Hollyrood House in Scotland was once the home of Mary, Queen of Scots.
Among other worthwhile places to visit are Oxford and Cambridge, both of which are university towns with many ancient buildings, and the Tudor home in which William Shakespeare was born. The main purpose of the passage is to （）.

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