This conversation is most likely to take place ______

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.