3Krashen,S.The Input Hypothesis:Issues and Implications [M].London:Longman, 1985.
4Swain,M.Communicative competence:Some roles of comprehensible input and comprehensible output in its development[A].In Gass S & Madden C eds.Input in Second Language Acquisition[C].Rowley, MA:Newbury House, 1985:235-253.