As per Stephen Krashen, “The effective language teacher is someone who can provide input and help make it _________ in a low anxiety situation.

According to Stephen Krashen's Second Language Acquisition theory, the correct answer is comprehensible.

Stephen Krashen proposed the Input Hypothesis, which states that language learners acquire language when they receive "comprehensible input"—that is, target language input that is slightly beyond their current level of competence (often represented as $i+1$), delivered in a low-anxiety environment (low affective filter).

Therefore, an effective language teacher provides input and helps make it comprehensible to facilitate natural language acquisition.