yellow空格在不定冠词a和名词box之间，因此可推测应填入修饰box的形容词，答案为yellow。

M: So, I’m guessing those yellow boxes I saw are for recycled newspapers?
W: Yes, that is correct, and it’s free of charge.
M: Wow, that’s good news! Do you recycle anything besides newspaper?
W: Oh yes, we recycle almost everything. Glass, plastic, paper...
M: Oh, so I can put like glass and plastic bottles in the box?
W: Sorry again. Things like that you have to bring to our collection centre.
M: And where is that?
W: Our main centre isn’t that far from you. It’s actually right on the East Side of Central Park.
M: That new blue building?
W: That’s the one!
M: Cool. Hey, what’s with all those different coloured boxes outside that place?
W: Oh, that’s for the different materials we recycle.  The blue is for metal, the green is for glass and plastics, and the yellow, of course, is for paper.
M: Hm, okay. I’ll try and manage to keep all that straight.
W: Oh, no need, they’re each labelled. M: Great. So which one would I put magazines in?
W: Actually, they don’t go in any of the bins.  Unfortunately, magazines can’t be recycled because of the material they’re made of. It’s such a waste. So would you be interested in volunteering?
M: Um, I’ll think about it. Could you send me some more info?
W: Absolutely. Along with the newspaper box, I’ll be sending you our booklet, ’Savvy’, that is S-A-double V-Y. It tells you about what you can do to protect the environment in your daily life. Plus it lists things you can do as a volunteer with our group.
M: Hey, that’s cool, thanks!
W: My pleasure. Do you have any other questions or concerns?
M: Nope, that’s it!