answer: #Person2# buys a pair of blue trousers made of cotton with 20 percent off for #Person2#'s son from #Person1#.
documents: #Person1#: Good morning. Is there anything I can do for you?
  #Person2#: Good morning. I am looking for a pair of trousers for my son. Could I see that pair hanging in the window?
  #Person1#: Sure sir. Is this the pair you meant?
  #Person2#: Yes, that's it. What are these trousers made of? My son's skin is quite sensitive, so I have to be careful about the material of the clothes he wears.
  #Person1#: These are made of cotton, sir. These are made by a famous children's brand called Wonder World. It's a very popular brand because of the good quality material.
  #Person2#: Oh, that's good. What other colors do these trousers come in? If you have blue, that would be great. Blue is my son's favorite color. I'd rather not have black or gray.
  #Person1#: Uh, these come in blue as well. Here you are, a blue pair.
  #Person2#: Thank you. And one last thing, how much do the trousers cost?
  #Person1#: Well, they were originally 150 yuan each, but they are now on sale 20% off.
  #Person2#: That's great. I'll take them.