听力原文：W: Roger, any problems in your Korean study? M: The biggest problem with me is the Korean vocabulary. It really makes me frustrated. The pronunciation and usage put me into great confusion as I keep forgetting them. W: I guess first of all you can narrow down the vocabulary sphere. I mean, try to learn 'core' vocabulary, the words with high frequencies of occurrence. M: That sounds quite reasonable. Do you think I can find in bookstores a book or dictionary where such kinds of words are listed? W: Yes, definitely. Another thing, the first several occurrences of strange words are very important. Words are best remembered if they are learnt quickly with a few presentations. You may not have much trouble in remembering swear words, may you? M: No. They're very impressive and quite memorable. I don't even need to practice them. W: That's it! For other words that don't have such a strong effect, yon have to make yourself highly attentive and sensitive. If not, later practice and repetition don't seem to work so well. M: I see. W: The last thing I'll say is that if you want to remember something for periods longer than a year or two, you need to space the presentations over quite long intervals of days, say 30 days. A more frequent interval doesn't promise you longer remembrance. M: Really? I have thought every word should be practiced as often as possible within a short time span. W: No. How the word is practiced is much more important than how often it is practiced. M: You really do me a great favor, Teresa. (23)