The average college student in America spent an estimated seven hundred dollars on textbooks last year. The National Association of College Stores reported more than five billion dollars in sales of textbooks and course materials. Association spokesman Charles Schmidt says electronic textbooks now represent just two to three percent of sales. But he says that is expected to reach ten to fifteen percent by 2012. Online versions are now available for many of the most popular college textbooks. E-textbooks can cost half the price of a new print textbook. But students usually lose access after the end of the term. And the books cannot be placed on more than one device   so they are not easy to share. So what do students think of e-textbooks? Administrators at Northwest Missouri State University wanted to find out. Earlier this year they tested them with five hundred students in twenty classes. The university is unusual. It not only provides laptop computers to all seven thousand of its full-time students. It does not require students to buy their textbooks either. They rent them to save money. The school aims to save even more by moving to e-textbooks. The students in the survey reported that downloading the books from the Internet was easy. They liked the idea of carrying lighter backpacks. And fifty-six percent said they were better able to find information. But most found that using e-textbooks did not change their study habits. And sixty percent felt they read more when they were reading on paper. In all, almost half the students said they still liked physical textbooks better. But the survey found that cost could be a big influence. Fifty-five percent said they would choose e-textbooks if using them meant their textbook rental fee would not increase. Roger Von Holzen heads the Center for Information Technology in Education at Northwest Missouri State. He tells us that administrators are disappointed with the e-textbooks now available because the majority are not interactive. He thinks growth will come when more digital books include video, activities, games and other ways to interact with the information. The technology is improving. But for now, most of the books are just words on a screen. The passage mainly tells us about   _  .
the development of e-textbooks different attitudes towards e-textbooks the sales of textbooks and course materials the differences between e-textbooks and physical text-books