Electronic books have changed the way many people read for pleasure. Now online textbooks are changing the way some students learn and some teachers teach. More than one hundred seventy-five thousand students attend the public schools in Fairfax County, Virginia, outside Washington. Last year, the school system used digital books in fifteen schools. This school year, middle schools and high schools changed from printed to electronic textbooks in their social studies classes. Luke Rosa is a history teacher at Falls Church High School. His students work on laptop computers at school. He explains the idea to them this way. "I mean, it's just like a regular textbook, except it's got it all online." Peter Noonan, an assistant superintendent   of schools, said, "The world's changing. And the online textbooks can change right along with the events that are happening." Digital books also cost less than printed textbooks, he said. A student named Melanie Reuter said, "I don't have to carry a textbook around, so that's nice." But another student said, "I don't like it because the Internet sometimes doesn't work." Students also need access to the Internet when they are not at school. About ten percent of students in Fairfax Country do not have a computer or online access at home. Public libraries in the country have free Internet. There are also after-school computer labs as well as computer clubhouse supported by the country. Middle school student Slieman Hakim is happy about that. He said, "My family only has one computer; my sister and I both do our homework on it. So I come here to do my homework. It's good." Other school systems in the area are also considering online textbooks. Which of the following is /are NOT used when students have social studies classes?
Paper textbooks. The Internet. Computers. Electronic textbooks.