一小车在平直的公路上匀速行驶时发动机的功率是50kW，速度是25m/s，小车的牵引力是____ N，它行驶100m做的功是____ J．

完形填空

    Mr. Wu is having a class in Class Five．He is asking students to think about(思考)  1  future 1ife．Here are some students' opinions(观点)．  

    Zhang Wei thinks people will live in the2like fish．because in the future people will 3organic silicon(有机硅)to breathe(呼吸)in the sea．And people will build 4and schools in the sea．Then they can see doctors and go to school．He

thinks life in the sea will be very 5  and comfortable．

    Luo Li thinks  6 in the future will be great．Every family will have a car．And these cars will 7  in the sky．People will drive cars to their offices．

  Wang Kai thinks machines like robots will do work for people,   8  people will have more 9  time to enjoy life．He thinks people will have short winter holidays but long  10holidays because the summer will be very long．

在⊙O中，r=13，弦AB=24，则圆心O到AB的距离为（　　）

世界上所有生物的生命都是有期限的，有的能活上百年，有的只能按天来计算，如：蜜蜂4周，狗13年，虎鲸90年，巨型龟150年，海蛤蛤410年。从中，我们可感悟到（    ）