把A，B，C三种金属片分别加入稀硫酸中，A，B表面有气泡产生，C无变化；把A加入B的硫酸盐溶液中，A表面析出B．则这三种金属的活动性顺序为（    ）

已知 $A$ ， $B$ 分别为双曲线 $C$ ： $\frac{x^2}{a^2}-\frac{y^2}{b^2}=1$ （ $a>0$ ， $b>0$ ）的左、右顶点， $P$ 是 $C$ 上一点，且直线 $AP$ ， $BP$ 的斜率之积为2，则 $C$ 的离心率为（    ）

根据课文，回答下列问题

所示杂志名称的由来与19世纪70年代开始的一次“革命”密切相关，这次“革命”是指(　　)

阅读理解。
    In a small town, there lived a doctor. He was good and kind. He was ready to go and help people. People always went to him when they were ill.
    Many years later, the doctor began to forget things. The people were afraid and little by little, they stopped going to him. The doctor saw his business (生意) wasn't as good as before. He thought, “Well, if I were the patients(people who don't feel well), I'd be afraid to go to me too. Maybe it's time for me to stop being a doctor. But if this town has no doctor, what will the people do when they become ill?”
    His wife heard him talking to himself and said, “Why don't you find a young doctor to take your place? Then people will have another good doctor to take care of them and I will get my husband back.”
    The doctor did as what his wife said. He found a very good young doctor to help the people. The doctor and his wife then had time to take long walks together, go dancing, go traveling and spend the rest of their days together.