Read the following passage, then choose the correct answer to each question.

London is the capital city of the United Kingdom. It is the largest city in Britain. It has got the population of about 7 million people. It is a very old city which was founded by the Romans.  London is famous for many things. The original area is the City. There are thousands of offices and banks but only a few people live here. The Tower of London was built in the 11th century. It was a prison but now it is a museum. You can see the Crown Jewels here. Tower Bridge is near the Tower of London. It was opened in 1894. Westminster Abbey is a beautiful church where the Coronation Ceremony takes place. Westminster Abbey is in the west of London, near the Houses of Parliament, where you can see and hear the well-known clock Big Ben.  Hyde Park is the most popular park in London. At Speaker’s Corner, anybody can speak about anything except the Queen. The Queen lives in Buckingham Palace. London stands on River Thames. There are 27 bridges over the Thames in London and 8 tunnels under the river. A quick and easy way to get to different places in the city is to use an underground train. Londoners call this means of transport the “tube”. There are many famous red buses in London called double-deckers and London taxis are called black cabs.

The Tower of London used to be ______.