By almost any measure, there is a boom in Internet-based instruction. In just a few years, 34 percent of American universities have begun offering some form of distance learning (DL), and among the larger schools, it’s closer to 90 percent. If you doubt the popularity of the trend, you probably haven’t heard of the University of Phoenix. It grants degrees entirely on the basis of online instruction. It enrolls 90,000 students, a statistic used to support its claim to be the largest private university in the country.While the kinds of instruction offered in these programs will differ, DL usually signifies a course in which the instructors post syllabi (课程大纲), reading assignments, and schedules on Websites, and students send in their assignments by e-mail. Generally speaking, face-to-face communication with an instructor is minimized or eliminated altogether.The attraction for students might at first seem obvious. Primarily, there’s the convenience promised by courses on the Net: you can do the work, as they say, in your pajamas (睡衣). But figures indicate that the reduced effort results in a reduced commitment to the course. While dropout rates for all freshmen at American universities is around 20 percent, the rate for online students is 35 percent. Students themselves seem to understand the weaknesses inherent in the setup. In a survey conducted for eCornell, the DL division of Cornell University, less than a third of the respondents expected the quality of the online course to be as good as the classroom course.Clearly, from the schools’ perspective, there’s a lot of money to be saved. Although some of the more ambitious programs require new investments in servers and networks to support collaborative software, most DL courses can run on existing or minimally upgraded (升级) systems. The more students who enroll in a course but don’t come to campus, the more the school saves on keeping the lights on in the classrooms, paying doorkeepers, and maintaining parking lots. And, while there’s evidence that instructors must work harder to run a DL course for a variety of reasons, they won’t be paid any more, and might well be paid less.What is the most striking feature of the University of Phoenix?