如图所示电路,要使电阻R1消耗的功率最大,应该把电阻R2的阻值调节到( )
A:R1+r
B:R1-r
C:r
D:0
At the top of the mountain, visitors can have a good of the whole city.
人喝醉了酒,走路摇晃、站立不稳,说明酒精已经麻痹了( )