如图所示电路,电源内阻不能忽略,R1阻值小于变阻器的总电阻,当滑动变阻器的滑片P停在变阻器的中点时,电压表的示数为U,电流表的示数为I.那么,滑片P由中点向上移动的全过程中( )
A:电压表的示数始终小于U
B:电流表的示数始终大于I
C:电压表的示数先增大后减小
D:电流表的示数先减小后增大
You'd better ask a ______, such as your aunt or sister, to look after your children while you are away.
观察下列各式:
13+23= 14 ×4×9= 14 ×22×32
13+23+33=36= 14 ×9×16= 14 ×32×42
13+23+33+43=100= 14 ×16×25= 14 ×42×52