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问题 选择题

人坐在沙发上比坐在木椅上感到舒服些，这是因为（　　）

A．弹簧的弹力与人体受到的重力平衡

B．弹簧的弹力与人体对沙发的压力平衡

C．弹簧的弹力减小了人体对沙发的压力

D．人体与沙发的接触面积较大

答案

A、弹簧的弹力与人体受到的重力是平衡力，但是不影响人体的舒服程度．不符合题意．

B、弹簧的弹力与人体对沙发的压力不是一个受力物体，不是平衡力．不符合题意．

C、人体对沙发的压力等于人体的重力，跟弹簧的弹力没有关系．不符合题意．

D、人坐在沙发上，人受到重力和支持力的作用，这两个力是平衡力，大小相等，重力不变，支持力不变，人受到的支持力实际上是沙发对人的压力，压力一定，坐在沙发上的受力面积大，人受到的压强小，人感到舒服．符合题意．

故选D．

单项选择题

The first and most important agents of socialization are the people who care for infants. In the earliest months, messages from nurturers constitute the child’’s basic understanding of the world around it. This is the infant’’s first introduction to the language that shapes perception and elicits emotion.Another powerful source of information and socialization is the friendship of peers. Peers are equals that one can deal with on the same level as oneself, whereas parents are superiors. The heavy emotional overlay of family relationships makes some kinds of learning difficult.Much formal socialization is placed in the hands of professionals. Teachers from kindergarten on are specifically designated agents of socialization. Ideally, a teacher is one who has both knowledge and the skills to present it. During the course of teaching their subjects, classroom instructors provide role models and attempt to convey the excitement of learning itself.In earlier times, parents, friends and teachers would comprise the list of primary childhood socializers. Children’’s books, comics and magazines might also have been mentioned as sources of information on norms and role models. Today one must add three powerful indirect or non-personal socialization agents: radio, movies and television. Many people learn about politics, form a vision of well-being, and develop attitudes towards others from what they see on the screen and hear through the speakers.

________are/is powerful indirect socialization agents.

A．Parents

B．Friends

C．Teachers

D．The media
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填空题

如图所示，质量为m的物体在与竖直方向成θ角的推力F作用下，沿竖直墙壁向上匀速运动。若物体与墙面间的摩擦因数为μ，则F的大小是_______________。
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