7Krashen, S D. 1982. Principles and practices in second language acquisition [M]. Oxford: Pergamon.
8Krashen, S D. 1985. The input hypothesis: Issues and implications [M]. London: Longman.
9Krashen, S D. 1994. The input hypothesis and its rivals [A]. In N Ellis (ed.) Implicit and explicit learning of languages [C]. London: Academic Press.
10Nobuyoshi, J and R Ellis. 1993. Focused communication tasks and second language acquisition [J]. ELT Journal, 47, 203-210.
