填空题

[听力原文] 11-15
The United States has long been called a melting pot because its population is made up of so many people from all over the world. The first immigrants in American history came from England. Immigrants from other countries then began arriving and are still coming. The greatest numbers came in the years 1880 to 1914. Between 1820 and 1973, the United States admitted over 46 million immigrants. Most came from Europe, but many also came from Latin America, Asia, Australia and Canada.

The United States has been called the melting pot because （） is made up of a lot of people come from all over the world.