题干
Mr．Li often drives his car to work，but he rides a bike there．
A：usually
B：sometimes
C：always
D：often
答案(点此获取答案解析）
B
Mr．Li often drives his car to work，but he rides a bike there．
A：usually
B：sometimes
C：always
D：often
、
是椭圆
的左、右焦点，
是该椭圆短轴的一个端点，直线
与椭圆
交于点
，若
成等差数列，则该椭圆的离心率为