—________
A:That is Jane.
B:This is Kangkang speaking.
C:I'm Mike.
D:She is Maria.
人体生命活动所需的能量主要来自( )
如图所示是一理想的自耦变压器,A、B端接交流电源,C、D端接负载电阻R,P为滑动触头,当P逆时针转动时,下列结论正确的是( )