问题补充:
---Why do you keep the windows open on such a cold day?
---There are so many students here, so we want to keep the air nice and .
A. cold
B. dry
C. cool
D. clean
答案:
A. cold
B. dry
C. cool
(答案→)D. clean
解析:在寒冷的天气把窗户打开是为了使空气清新和干净,clean表示此意,故本题选D。