题干

先后用相同材料制成的橡皮条彼此平行的沿水平方向拉同一质量为m的物块,且每根橡皮条的伸长量均相同,物块m在橡皮条拉力的作用下所产生的加速度a与所用橡皮条的数目n的关系如图所示.下列措施中能使图线的截距变化的是(  )

A:仅改变橡皮条的伸长量

B:仅改变物块的质量

C:仅改变橡皮条的劲度系数

D:仅改变物体与水平面的动摩擦因数

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D

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    Several days ago, Brenda had a car accident that led to one of her legs being cut off. Since then she didn't talk to anyone."I wish I could bring her friends to visit her," said Brenda's mother. "But it's a long bus trip." The nurse smiled, "Don't worry. We have a plan."Later that day, the nurse had taken Brenda to another room. "Here's your new roommate, Annie Wiggle-Do," the nurse introduced a dark-hair teenager on the other bed.

    As soon as the nurse left, she jumped out of her bed with her only foot and sat at the other end of Brenda's bed, "I lost my leg from bone cancer," she said. "What happened to yours?" Brenda was so shocked that she couldn't say a word. "You're lucky." Annie continued. "You've still got your knee. They had to take mine."

    "I'd like to have a chat with you, but my friends are coming any time now, so I have to get ready." Annie said when she took off her hair! Her head was completely bald(秃头的).

    "Oh, I forgot to tell you, the medicine they gave me to kill the cancer also killed my hair." Annie looked out her wigs(假发), brown and yellow, short and long, straight and curly."That's why I thought up 'Annie Wiggle-Do'." Annie smiled. "Get it? Any wig will do? Annie Wiggle-Do?" "When Annie's friends came, she introduced Brenda to them all. Before long, Brenda started chatting with Annie and her friends. They didn't make her feel like a strange person at all!

    The girls shared their names with each other. When it was time to go to bed, Brenda said, "Good night, Annie-Wiggle-Do. Can't wait till morning."