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问题 选择题

物体在合力F的作用下，由静止开始运动，若力F随时间t按图中的情况变化，则在0～t1的时间内物体运动的（　　）

A．加速度不变，速度增大

B．加速度不变，速度减小

C．加速度和速度都变小

D．加速度减小，速度增大

答案

根据牛顿第二定律a=

F
m
可知随着F的减小，加速度在减小，F的方向不变且与速度方向相同，所以物体一直做加速运动，故选D．

选择题

京沪高铁于2011年6月30日正式运营。高铁以其舒适安全快捷的性能，低于汽车的价格，给公路交通和民航交通带来了巨大的挑战。北京至上海的快运汽车票价最有可能作出的反应是（  ）    

A．下调，因为高铁与汽车是互补商品

B．上调，因为高铁与汽车是互为替代商品

C．上调，因为高铁与汽车是互补商品

D．下调，因为高铁与汽车是互为替代商品
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补全对话，情景问答
从方框中选出适当的句子补全对话，有两项是多余的。
Jane: Excuse me!     1    
Jack: Sure! What question?
Jane: What would you do if you wanted to be friends with a new student?
Jack: I'd wait for her to introduce herself to me.     2     
Jane: Because it could tell me your personality.
Jack: Well, what do you think I'm like?
Jane: You are probably a shy person.
Jack:     3   _ I don't like talking to a group.
Jane :     4  _ But your friends say you are a good listener.
Jack: Absolutely! I like listening to others. How about you? Are you shy, too?
Jane: I'm afraid not.     5    I have lots of friends and I enjoy the company of other people.
Jack: I think so.
A. May I ask you a question?
B. Why do you ask me this question?
C. Maybe you are right.
D. I think I'm outgoing and fairly confident.
E. That's why you don't want to introduce yourself first.
F. I don't think so.
G. Maybe that's a good idea.
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