Thank you very much, Dr. Harley, for introducing some of the language teaching methods. Now let's move on to something a bit theoretical. Since second language acquisition and teaching are a fascinating area for researchers, are there any theories to explain second language acquisition? Yes, many theories and models have been put forward by researchers so far. Today, I'd like to mention the five hypotheses proposed by Stephen Krashen. OK. The five hypotheses, or what he calls, the monitor model of second language learning. What does it mean? OK. The first hypothesis is the acquisition and learning distinction hypothesis. According to Krashen, children acquire their first language largely unconsciously and automatically, but adults could only learn a second language consciously and effortfully. And adults could indeed acquire the second language, at least in part.