题目

Do you know there is a special(特别的) job? The worker is not a man but a dog. They’re a kind of dogs. They are like the eyes of blind(盲的) people. So we call them “seeing eye dogs”.These dogs usually need to learn for two or three years. And then they live with blind people. Their job is to help blind people walk around（四处走）.They know how to cross the street（街道）.They can also avoid dangers, like cars and bikes in the street.Sometimes you can see these dogs with blind people. Just like other dogs, seeing eye dogs are very cute. But they are not only pets. They wor质量为1 kg的小球从距地面高0.45 m处自由下落到地面上，反弹后上升的最大高度为0.20 m，小球与地面接触的时间为0.05 s，不计空气阻力，g取10 m/s2.则在触地过程中，小球受到合力的冲量大小为（　　）?A.1.0 N·s            B.1.5 N·s            C.5.0 N·s              D.5.5 N·s