Nowadays we can see more and more electric bikes in the street. Electric bikes are easy to1. They run fast and make no pollution. So they become very2in many big cities in China.But the electric bikes also cause more traffic accidents. So China plans to make a new rule3the electric bike riders. If an electric bike is heavier than 40 kilos and can go faster than 20 kilometers an hour, its rider must get a license(许可证). It means riders have to pass driving tests4they ride their electric bikes on the road.

    People have different ideas about the plan. Some welcome the plan because they think it will make the street much safer. But some are not happy with the new rules at all. One rider said, “I don't want to get a license or anything. That's too much5.” What's your idea?

若用同一显微镜观察同一标本4次，每次仅调整目镜、物镜和细准焦螺旋和遮光器，结果得到下面亮度相同的各图．试问其中通光孔通光量最大的是（　）

若$a_i,b_i\in R_{+}\left(i=1,2,3,...,n\right)$  ，求证$\left(a_1{b}_1+···+a_n{b}_n\right)\left(\frac{a_1}{b_1}+···+\frac{a_n}{b_n}\right)\ge {\left(a_1+···+a_n\right)}^2$  .

通过抓关键词了解和掌握知识是学习历史的有效方法之一，与“路易十六”、“巴士底狱”、“《人权宣言》”三个关键词都有关的历史事件是（   ）