As a language teacher, which of these options will be most applicable for facilitating second language acquisition according to the affective filter hypothesis?

According to Stephen Krashen's Input Hypothesis, providing 'comprehensible input' in second language learning implies that instruction should transition from:

Positive transfer (or positive interference) of learning helps in the acquisition of the ____

What is the term coined by Stephen Krashen to describe a stage where a learner is at stage 'i' and language acquisition takes place when they are exposed to a slightly higher level at stage 'i + 1'?