题干

在“探究滑动摩擦力的大小与什么因素有关”的实验中.同学们提出了以下猜想:

A.滑动摩擦力的大小与接触面受到的压力大小有关

B.滑动摩擦力的大小与接触面的粗糙程度有关

C.滑动摩擦力的大小与接触面面积的大小有关

某小组根据猜想进行了以下实验,如图所示(图中的木块、长木板完全相同).

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同类题3

    "Can I see my baby?" the happy new mother asked. When the baby was lying in her arms and she moved the cloth to look upon his tiny face, she gasped(吃力地喘着气). The doctor turned quickly and looked out of the hospital window. The baby had been born without ears. Luckily, time proved that the baby's hearing was perfect. Though the misfortune(不幸)happened to him, he grew into a handsome boy. Yet he felt ashamed when he communicated with others.
    "You should get in touch with other young people," his mother told him, with a kindness in her heart. The boy's father talked with the family doctor about his ears. "Could nothing be done?"the father asked. "I believe I could give him a pair of outer ears, if they could be got," the doctor replied.
    Two years went by. One day, his father said to the son, "You are going to the hospital, Son. Mother and I have someone who will donate the ears you need, but it's a secret."The operation is a big success. Later he married and entered the diplomatic(外交的) service. One day, he asked his father, "Who gave the ears? Who gave me so much? I could never do enough for him or her."
    "You could, my son," said the father, "but the agreement was that you are not to know…not yet."
    The years kept their secret, but one of the darkest days did come. He stood with his father over his mother's casket(棺材). Slowly, the father stretched forth(伸出) a hand and raised the thick, reddish brown hair to reveal the mother had no outer ears.
    "Mother said she was glad she never let her hair be cut," his father whispered gently, "and nobody ever thought mother less beautiful, did they?"