中国大学MOOC: 1. River ThamesThe River Thames is the second longest river in the United Kingdom and the longest river entirely in England, rising at Thames Head in Gloucestershire, and flowing into the North Sea at the Thames Estuary. It has a special significance in flowing through London, the capital of the United Kingdom, although London only touches a short part of its course. The river is tidal in London with a rise and fall of 7 meters (23 ft) and becomes non-tidal at Teddington Lock. The catchment area covers a large part of South Eastern and Western England and the river is fed by over 20 tributaries. The river contains over 80 islands, and having both seawater and freshwater stretches supports a variety of wildlife.The river has supported human activity from its source to its mouth for thousands of years providing habitation, water power, food and drink. It has also acted as a major highway both for international trade through the Port of London, and internally along its length and connecting to the British canal system. The river’s strategic position has seen it at the centre of many events and fashions in British history, earning it a description by John Burns as “Liquid History”. It has been a physical and political boundary over the centuries and generated a range of river crossings. In more recent time the river has become a major leisure area supporting tourism and pleasure outings as well as the sports of rowing, sailing, kayaking, and punting. The river has had a special appeal to writers, artists, musicians and film-makers and is well represented in the arts. It is still the subject of various debates about its course, nomenclature and history.The River Thames has twenty-seven bridges. But Tower Bridge, the first bridge over theThames as you travel to London from the sea,is the most famous of them all. What makes TowerBridge so exciting? Why do visitors from all over the worldwantto see it?The thing that is surprising about Tower Bridge is that it is open in the middle. It does this to let the big ships through to the Pool of London.lf you are lucky enough to see the bridge with its two openingarms high in the air,you will never forget it.On its north side stands the Tower of London itself.Although they look like the same age,the Tower is almost a thousand years old,and Tower bridge is only about one hundred.It was built in the 1890s. 2.Why is Tower Bridge open in the middle?