两个电阻R1、R2,将它们串联时,功率比P1∶P2=5∶7。在电源电压不变时,如果将它们并联时,功率比P1∶P2=______。
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将10 W、10 Ω和25 W、1Ω的两个电阻串联起来,所允许流过的最大电流为______A。
The Backbone of North America refers to the ____.
Appalachian Mountains
B. Rocky Mountains
Cascade Mountains
D. Nevada Mountains
Which of the following city has the lowest crime rate?
A. Chicago
B. New York
C. Philadelphia
Detroit
The City of Big Shoulders refers to _____.
A. New York
B. Los Angeles
C. Houston
D. Chicago