First listen and then answer the question.
How many people visited the Great Exhibition of 1851?

    Perhaps the most extraordinary building of the nineteeth century was the Crystal Palace, which was built in Hyde Park for the Great Exhibition of 1851. The Crystal Palace was different from all other buildings in the world, for it was made of iron and glass. It was one of the biggest buildings of all time and a lot of people from many countries came to see it. A great many goods were sent to the exhibition from various parts of the world. There was also a great deal of machinery on display. The most wonderful piece of machinery on show was Nasmyth's steam hammer. Though in those days, traveling was not as easy as it is today, steam boats carried thousands of visitors across the Channel from Europe. On arriving in England, they were taken to the Crystal Palace by train. There were six million visitors in all, and the profits from the exhibition were used to build museums and colleges. Later, the Crystal Palace was moved to South London. It remained one of the most famous buildings in the world until it was burnt down in 1936.