1.引言语言习得理论的一个中心问题是语言学习者所遇到的以前未知之语言材料对学习该语言的作用如何。学习者接触的潜在目标语的语言材料总括起来被称为输入。人们公认,输入使第二语言学习者的目标语知识逐步发展成为可能(Wagner-Gough和Hatch,1975)。显然,语言输入是第一和第二语言习得的必要条件。正如Wode(1981)所说, 1. Introduction A central issue in the theory of language acquisition is the role played by language learners of previously unknown language materials in learning the language. The language material of the potential target language that the learner touches is collectively referred to as input. It is accepted that it is possible for input to progressively develop SLA knowledge (Wagner-Gough and Hatch, 1975). Obviously, language input is a necessary condition for first and second language acquisition. As Wode (1981) said,