题目

用一张长40厘米、宽20厘米的长方形纸围成一个圆柱，不管怎么围（接头处不计），圆柱的侧面积都是800平方厘米。（） 答案：正确Usually a meteorological observatory (气象台) _____ air quality in urban areas from one to five: excellent, fairly good, slightly polluted, poor, and dangerous. A．identifiesB．purifiesC．classifiesD．clarifies