问题
不定项选择
如图所示是一火警报警器的部分电路示意图，其中R2为半导体热敏材料制成的传感器，其电阻R2随温度t变化的图线如图所示。电流表为值班室的显示器，a、b之间接报警器。当传感器R2所在处出现火情时，显示器的电流I和报警器两端的电压U的变化情况是
A．I变大，U变大
B．I变大，U变小
C．I变小，U变大
D．I变小，U变小
答案
答案：D
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如图所示是一火警报警器的部分电路示意图，其中R2为半导体热敏材料制成的传感器，其电阻R2随温度t变化的图线如图所示。电流表为值班室的显示器，a、b之间接报警器。当传感器R2所在处出现火情时，显示器的电流I和报警器两端的电压U的变化情况是
A．I变大，U变大
B．I变大，U变小
C．I变小，U变大
D．I变小，U变小
答案：D
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| Jane Scott is fourteen years old and last year she began to study in a middle school. She likes dancing and singing and spends a lot of time on them. (1)_____________. She thinks it difficult to learn. Once she failed the math exam, and now she decides to give it up. (2)_____________. It was Sunday. Mr. Scott gave a call to his sister. She teaches math in another school. He hoped she would come and tell his daughter how to learn math. The woman came quickly and said, "You're a clever girl, Jane. (3)______________." "I'm afraid I can't, Aunt," said Jane. "I am not interested in math at all." "I don't think so," said the woman. "I was good at it when I was a girl. You can do more exercises and practice a math problem again until you make it. Well, here's a math problem. Think it over and practice it again and again, then you will work it out." "OK," said the girl, "Let me have a try." About an hour later Jane took the exercise book to her aunt and said," (4)____________." "Well done!" her aunt said happily, "What answer did you get?"
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