A:{x|x+3=3}
B:{(x,y)|y2=﹣x2,x,y∈R}
C:{x|x2≤0}
D:{x|x2﹣x+1=0,x∈R}
All schools in our province________new English textbooks to improve students'listening,speaking,reading and writing abilities three years ago.
俄罗斯在世界上占有重要地位的产业是( )
下图是某国局部地区人口分布示意图,读图,完成下列各题。
该化学反应的基本类型为____;