A:
B:a≤-2或1≤a≤2
C:a≥1
D:-2≤a≤1
—How far is it from Beijing to Haikou?
—It's a______ flight from Beijing to Haikou.
证明定理:等腰三角形的两个底角相等.(画出图形、写出已知、求证并证明)
下列叙述中,不是地图基本要素的是( )