答案:Monitor Theory. According to the tenets of the theory, learners acquire language by being exposed to language that contains structures just beyond (i.e., + I) their current level of development. As a construct, i + 1 has intuitive appeal, but unfortunately is not operationalizable as a research construct —mean ing a researcher cannot create an experiment saying "Here's the learner's i and now I'm going to give that learner language containing + I to see if he/she learns the + l." The problem, of course, is in establishing what i is and also what i + l would be. i + 1 fell away as a major construct within SLA as Monitor Theory's appeal began to wane.