Passage TwoQuestions 26 to 30 are based on the following passage. Online learning is also called distance education，which helps students who take classes by computer over the Internet to learn certain courses and earn a degree. And it has become more and more popular with both young people and educational institutions. The School of Continuing and Professional Studies of New York University in Manhattan began online classes in 1992. Its Virtual School has taught more than 10,000 students from across the United States and other countries. Last year，the school launched NYU Online. It offers NYU’s first online programs for a bachelor’s degree. Programs are offered in three areas：leadership and management，information systems management and social sciences. The classes are highly interactive，where students communicate with each other and their teachers. Some classes require students to log in at the same time 80 they can attend live lectures by a professor. Students can also ask questions and work together on team projects. The cost to attend NYU Online depends on how many classes a student is to take. It costs as much as fifteen thousand dollars a year. NYU offers no financial aid for international students in this program. If you are interested in the program，you can get more details at the website：www. nyu. edu. Many other schools，too，offer online education. Students should be especially careful of programs that offer a degree in return for little or no work. These are known as diploma mills，and are illegal in the United States. Educational advisers also say that before you enter any program，make sure the work will be recognized in your country. You should also make sure the schools you are considering are officially approved. The payment for online programs of NYU is based on______.

A. the number of classes a student attends
B. the number of students a professor instructs
C. the number of semesters a student spends
D. the number of presentations a student makes