Ответ:
1 Amy is buying souvenirs because she is having a walk in the centre of London on her first day there.
2 William is studying the map of London because he is visiting his friends in London.
3 Melanie and Amy are buying Caribbean folk costumes because they are taking part in the Notting Hill carnival.
4 William is learning the British driving rules because he is driving the car on the way from London to Edinburgh.