London has a population of about 7,500,000. It lies on the river Thames. From about 1800 until World War II, London was the biggest city in the world, but now, there are many cities which are much bigger. London is famous for many things. Tourists come from all over the world to visit its historic buildings such as St. Paul's Cathedral, the Houses of Parliament, where you can see and hear the famous clock, Big Ben. They also come to visit its theatres, its museums its many shops such as Harrods, where you can buy anything. Like many big cities, London has problems with traffic and pollution. Over 1,000,000 people a day use the underground, but there are still many cars on the streets. The air isn't clean, but it is cleaner than it was 100 years ago. London is famous for its fog or "smog" which is a mixture of smoke and fog. 1. Is London the biggest city in the world? 2. What is Harrods? 3. Where can you hear and see the famous clock, Big Ben?