Yes. His fourth hypothesis is the comprehensible input hypothesis. In order to move from one stage to the next, the learner must understand the meaning and the form of the input. This emphasizes the role of comprehension. And finally, the active filter hypothesis. This suggests attitude and emotional factors are also important in second language acquisition. I guess Krashen's model has provided a useful framework for second language learning. Yes, it indeed has and it has also proved to be one of the most influential theoretical approaches to teaching a second language. OK, Dr. Harley. Thank you once again for talking to us about second language acquisition. Pleasure.