1Keller. J. M. Motivational Design of Instruction. In C. M. Reigeluth (Ed.). Instructional - Design Theories and Models: An Overview of Their Current Status [M]. Hillsdale. New Jersy: Lawrence Erlbaum Associates Publishem, 1983: 126.
2Krashen, S. D. The Input Hypothesis: Issues and implications [M]. London: Longman, 1985: 47.
