What is the passage mainly about? A. Life of the working class in the United States in the 19th centuryĐoạn văn34/40What is the passage mainly about? Life of the working class in the United States in the 19th century Big businesses in the United States in the 19th century Significant improvements in the United States The role of the middle class in the United States in the 19th centuryGiải thíchChọn đáp án C