Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions

At the age of sixty-five, Laura Ingalls Wilder began writing a series of novels for young people based on her early experiences on the American frontier. Born in the state of Wiscosin in 1867, she and her family were rugged pioneers. Seeking better farm land, they went by covered wagon to Missouri in 1869, then on to Kansas the next year, returning to Wisconsin in 1871, and traveling on to Minnesota and Lowa before settling permanently in South Dakota in 1879. Because of this continuing moving, Wilder's early education took place sporadically in a succession of one-room schools. From age thirteen to sixteen she attended school more regularly although she never graduated.

At the age of eighteen, she married Almanzo James Wilder. They bought a small farm in the Ozarks, where they remained for the rest of their lives. Their only daughter, Rose, who had become a nationally known journalist, encouraged her mother to write. Serving as agent and editor, Rose negotiated with Harper's to publish her mother's first book, Little House on the Big Woods. Seven more books followed, each chronicling her early life on the plains. Written from the perspective of a child, they have remained popular with young readers from many nations. Twenty years after her death in 1957, more than 20 million copies had been sold, and they had been translated into fourteen languages. In 1974, a weekly television series, "Little House on the Prairie", was produced based on the stories from the Wilder books.

Câu 2 : The word “they” in the second paragraph refers to ______ .

A. young readers

B. many nations

C. the plains

D. more books