关于滑动变阻器和电阻箱的下列说法中，正确的是（ ）
A．它们都能任意连续改变接入电路的电阻大小
B．它们都能显示接入电路的电阻大小
C．它们都是靠改变导线的粗细来改变电阻的
D．它们都能逐渐改变所在电路的电流大小
A、电阻箱能表示出连入的阻值，但不能任意地改变连入电路的电阻，所以A错误；
B、滑动变阻器能连续地改变接入电路中的阻值，但不能读数，所以B错；
C、滑动变阻器靠改变连入电路中电阻丝的长度来改变电阻的大小的，所以C错误；
D、滑动变阻器能逐渐改变电阻的大小，故能逐渐改变电路中电流的大小；而电阻箱虽然不能连续改变电阻的大小，但是，电阻箱的电阻也有大有小，故也能逐渐改变电阻的大小；故D正确．
故选D．
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| Free to Fly with the Wind One windy sprind day,I observed young people having fun by flying their kites in the wind.Colorful 1 of varying shapes and sizes filled the blue and clean skies like beautiful birds 2 . As the strong winds blew against the kites,a 3 kept them in control. Instead of blowing away with the wind,they went up against it to achieve great 4 .They shook and pulled,but the control string and the long tail kept them under 5 , facing upward and against the 6 . As the kites struggled and trembled against the string,they seemed to be saying,"Let me go!Let me go!I want to be 7 !"They flew beautifully even as they fought the control of the string.Finally,one of the kites 8 in breaking loose."Free at last,"it seemed to be saying,"Free to fly with the wind." Yet freedom from control simply put it at the 9 of an unsympathetic wind.It 10 ungracefully to the ground and landed in a wild mass of weeds."Free at last"-free to 11 powerlessly in the dirt,and to be blown 12 along the ground... How we are like kites sometimes!The Heaven gives us adversities(逆境),limits and rules to 13 from which we can grow and gain strength.Control is a 14 opponent to the winds of opposition.We can never go up high enough to achieve our goals sometimes if we lose our necessary 15 or the rules. | ||||
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