According to Krashen's “Input Hypothesis”, learners acquire language as a result of comprehending input addressed to them. Krashen brought forward the concept of “i + 1” principle, i.e. the language that learners are exposed to should be just far enough beyond their current competence that they can understand most of it but still be challenged to make progress. Input should neither be so far beyond their reach that they are overwhelmed, nor so close to their current stage that they are not challenged at all.

本题考查Krashen的“输入假说”。 输入假说是其语言习得理论的核心部分。 他认为， 只有当习得者接触到“可理解的语言输入”， 即略高于他现有语言技能水平的第二语言输入， 而他又能把注意力集中于对意义或对信息的理解而不是对形式的理解时， 才能产生习得。 这就是他著名的i + 1公式。 i代表习得者现有的水平，1代表略高于习得者现有水平的语言材料。 根据克拉申的观点， 这种i + 1的输入并不需要人们故意地去提供， 只要习得者能理解输入， 而他又有足够的量时， 就自动地提供了这种输入。