A：天然气
B：核能
C：石油
D：风能
We don't want to speak badly or ______ in front of the class.
There are 15 _____ in the hospital. They are all friendly to the patients.
看图列算式．
○○○○○○○○○○○○
从第二行移（ ）个圆给第一行，两行圆的个数就同样多。
，过其右焦点且垂直于实轴的直线与双曲线交于M、N两点，O是坐标原点.若
，则双曲线的离心率为 （ ）.