如图所示，甲、乙两物体叠放在水平面上，用水平力F拉物体乙，它_爱下问搜题

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问题选择题

如图所示，甲、乙两物体叠放在水平面上，用水平力F拉物体乙，它们仍保持静止状态，甲、乙接触面也为水平，则乙物体受力的个数为（　　）

A．3个

B．4个

C．5个

D．6个

答案

与物体发生相互作用的有地球、水平桌面及甲物体；则乙物体受重力、桌面的支持力、甲对乙的压力及水平力F；因在拉力作用下，物体乙相对于地面有相对运动的趋势，故乙受地面对物体乙的摩擦力；而甲与乙相对静止，故甲对乙没有摩擦力；故乙受五个力；

故选C．

完形填空

A long time ago, there was an emperor. One day he told his horseman that if he could ride on his horse and 1 as much land area as he liked, he would give him the area of land he had covered. 2 enough, the horseman quickly jumped onto his horse and 3 as fast as possible to cover as much land area as he could. He 4 riding and riding, whipping the horse to go as fast as possible. Even when he was 5 and tired, he did not stop 6 he wanted to cover as much area as possible. When he at last covered a large amount of land, he was exhausted and was 7 . Then he asked himself, “Why did I 8 myself so hard to cover so much land area? Now I am dying and I only 9 a very small area to 10 myself.”
The above story is 11 to the journey of our 12 . We push ourselves very hard every day to make more 13 , to gain power or recognition. We neglect our 14 , time with our family and to appreciate the surrounding 15 and the things we love to do. One day 16 we look back, we will 17 that we don’t really need that much, 18 then we cannot turn back time for what we have 19 .
Life is not about making money. Life is definitely not about work! Work is only 20 to keep us living so as to enjoy the beauty and pleasures of life.

D．Interesting

D．succeeded in

C．discoveries

解答题

维生素既参与构成人体细胞，又能为人体提供能量．______．