There are twenty seven bridges over the River Thames．And the Tower Bridge is the first bridge you have to pass if you go to London from the sea．It is close to the Tower of London，from which it got its name．It is a symbol （象征） of London．

The Tower Bridge was set up over the River Thames in London in 1894and is one of the finest and most famous bridges in the world．It is the only bridge over the Thames that can be raised and opened in the middle．The middle part can be raised to let the huge ships pass．It used to be raised about 50times a day，but now it is raised only 4to 5times a week．If you are lucky enough to see the bridge with its two arms open high in the air，you will never forget it．

The Tower Bridge stands just on the south side of the Tower of London．People often think they are of the same age．But in fact，the Tower of London was built a thousand years ago，while the Tower Bridge only has a history of over one hundred years．

The Tower Bridge was first painted chocolate brown．Then in 1977，it was painted red，white and blue．Its picture also appeared in the opening of the 2012Summer Olympic Games held in London．So come to visit the famous bridge．You are sure to have a wonderful experience．

41．The color of the Tower Bridge hasn't changed for more than a hundred years． 　 　

42．In 1894，the Tower Bridge was built in London． 　 　

43．The Tower of London has a much longer history than the Tower Bridge． 　 　

44．The Tower Bridge is now raised less often than in the past． 　 　

45．This passage means to introduce the Tower of London． 　 　．