7Swain, M. 1985. Communicative competence: some roles of comprehensible input and comprehensible output in its development [A]. In S. M. Gass &C. G. Madden (eds.) 1985:235-253.
8Van Lier, L. 1994. Forks and hope: Pursuing understanding in different ways [J]. Applied Linguistics 15: 328-346.
9Varonis, E. M. & S. Gass. 1983. Target language input from non-native speakers [A]. Quoted in M.Long & P. Porter. 1985.
10White, L. & P. Lightbown. 1984. Asking and answering in ESL classes [J]. Canadian Modern Language Review 40: 228-244.