People of Hispanic origin were on the North American continent centuries before settlers arrived from Europe in the early 1600s and the thirteen colonies joined together to form the United States in the late 1700s. The first census of the new nation was conducted in 1790, and counted about four million people, most of whom were white. Of the white citizens, more than 80% traced their ancestry back to England. There were close to 700,000 slaves and about 60,000 "free Negroes". Only a few Native American Indians who paid taxes were included in the census count, but the total Native American population was probably about one million.　　By 1815, the population of the United States was 8.4 million. Over the next 100 years, the country took in about 35 million immigrants, with the greatest numbers coming in the late 1800s and early 1900s. In 1882, 40,000 Chinese arrived, and between 1900 and 1907, there were more than 30,000 Japanese immigrants. But by far, the largest numbers of the new immigrants were from central, eastern, and southern Europe.　　An enormous amount of racial and ethnic assimilation has taken place; the United States. In 1908, play-write Israel Zangwill first used the term "melting pot" to describe the concept of a place where many races melted in a crucible and re-formed to populate a new land. Some years during the first two decades of the 20th century, there were as many as one million new immigrants per year, an astonishing 1 percent of the total population of the United States.　　In 1921, however, the country began to limit immigration, and the Immigration Act of 1924 virtually closed the door. The total number of immigrants admitted per year dropped from as many as a million to only 150,000. A quota system was established that specified the number of immigrants that could come from each country. It heavily favored immigrants from northern and western Europe and severely limited everyone else. This system remained in effect until 1965, although after World War II, several exceptions were made to the quota system to allow in groups of refugees.　　22. Why did the author write the passage?　　(a) to outline the ways immigration has been restricted　　(b) to emphasize the impact of migrants from Europe　　(c) to explain and give examples of the concept of a "melting pot"　　(d) to summarize the main features of immigration　　23. According to the passage, which ancestry predominated at the time of the first census?　　(a) Native Americans　　(b) Negroes　　(c) English　　(d) Hispanic　　24. The word "ancestry" in line 5 is closest in meaning to　　(a) origins　　(b) inheritance　　(c) color　　(d) freedom　　25. The word "their" in line 5 refers to which of the following　　(a) immigrants　　(b) people of Hispanic origin　　(c) white citizens　　(d) Native Americans