A:that; that
B:that; whe
C:when; that
D:when; whe
读等高线地形图,回答问题.
Can you hear a duck? Yes.
已知双曲线x2a2-y2b2=1a>0,b>0的两焦点为F1,F2,过F2作x轴的垂线交双曲线于A,B两点,若△ABF1内切圆的半径为a,则此双曲线的离心率为( )
读长江水系图,完成下列要求.