参考答案： Distance learning is a formal educational process that breaks the traditional mode of classroom teaching. There are two key differences between traditional education and distance learning. Distance learning adds flexibility and availability, regardless of time, place, or pace of learning.
Here an instructor teaches，and somewhere else a student learns，regardless of barriers of time or place. Distance learning reaches out to non-traditional students who must fit their studies around workplace, family responsibilities, and geographical barriers, etc. Students can be at satellite campuses, at the workplace, or at home. Instruction may take place in real time or on a time- delayed basis. Interactivity between student and instructor, as well as among students themselves can be built into the program. The outcome can be a bachelor’s degree or a master’s degree, professional certification, on-the-job training, or life-long learning.
A number of technologies can be employed in distance instruction，depending on what is most appropriate for the subject and the targeted group of students. In addition, students usually progress through the course at their own speed.
Distance learning modes are as varied and numerous as the courses themselves. The most effective course in distance learning always knows how to combine the use of media with the nature of the subject being taught.
Generally speaking, there are three basic transmission modes in distance learning: live TV broadcast, transmission of complete or compressed information as well as computer-based instruction. Of course, all these modes can also be used in combination. For instance, live Education broadcast via satellite or the World Wide Web can be added in courses conducted primarily with videotapes.
In addition, instructor-student interactivity as well as student-student interactivity is also an important part of the learning process. There are a number of supportive technologies that can help promote interactivity in the distance learning environment, including electronic bulletin boards, internet, email, fax, Internet Relay Chat (IRC)，telephone and snail mail.