听力原文：M: Now that you are all here, let me show you around this plant, and if you liste

n closely, you might learn something about glass and crystal.

W: I had nothing about the structure of crystal before I have just learned in our science class. I always thought there was crystal in glass.

M: Well, real crystal is generally a hard substance in which the atoms are arranged in a highly ordered structure much like the framework of a skyscraper.

W: Does that mean in ordinary glass the molecules are not ordered？

M: That's right, but most of the glass made here is actually lead crystal or glass with a high lead content.

W: Lead？ Isn' t lead poisonous？

M: What it does is to make a very good quality glass. You will see several samples of glass on the tour. If everyone is ready now, please follow me.

W: I am supposed to hand in a paper in this aspect after the tour.

(20)

A．At an industrial site.

B．In a classroom.

C．At a department store.

D．In a laboratory.