下面文章中有3处需要添加小标题。请从以下选项（A、B、C和D）中选出符合各段意思的小标题
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.
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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.
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They will do all the heavy and dangerous work, and be put in hospitals, schools and offices.
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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.
水平抛出，不计空气阻力，落地点到抛出点的水平距离为s．若只将小球水平抛出的初速度变为
，则金属小球落地点到抛出点的水平距离为
