若等腰三角形的一个内角是40°，则它的顶角是（　　）

    Man has been interested in robots for quite some time. Scientists are always inventing new and good robots, which will play an important role in our future lives.

    ____

    They will take over jobs such as preparing meals, washing dishes, and sweeping the floor, so that we will have more free time to have fun.

    ____

    They will do all the heavy and dangerous work, and be put in hospitals, schools and offices.

    ____

    Whenever we feel sad, lonely or upset, we can have a chat with a robot. Robots will not only be good friends but they will also offer us good advice.

    In conclusion, robots will be more and more intelligent and will benefit us in many ways.

A. Robots will be our friends.

B. Robots will help us with our work.

C. Robots will be of help in doing housework.

D. Robots will replace humans in many ways.

制作洋葱表皮临时装片和口腔上皮细胞临时装片时，都是先在载玻片上滴加几滴清水

世界大多数农作物和动植物都能在我国找到适合生长的地区，是因为我国（　　）

如图所示，斜槽轨道下端与一个半径为0.4m的圆形轨道相连接．一个质量为0.1kg的物体从高为H=2m的A点由静止开始滑下，运动到圆形轨道的最高点C处时，对轨道的压力等于物体的重力．求物体从A运动到C的过程中克服摩擦力所做的功（g取10m/s²）．