听力原文：W: Before we begin the tour of the factory, do you have any more questions? M: Yes, I have one. I' d like to know the exact difference between crystal and glass. W: Well, real crystal is generally a hard substance in which the atoms are arranged in a highly ordered structure, much like the frame-work of a skyscraper. M: Does it mean that in ordinary glass the molecules are not ordered? W: That' s right. But most of the glassware made here is actually lead crystal or glass with a high lead content. M: Lead? Isn' t lead poisonous? W: No, when it's mixed with glass. What it does is to make a very good quality glass. I'll be showing you samples of several kinds of glass on our tour. If everyone is ready, we'll begin now. Please follow me. This conversation is most likely to take place ______