A:that
B:the one
C:those
D:one
在△ABC中,D、E分别是AB边和AC边的中点,若DE的长是2, 则BC的长为( )
—After a long sleep,I feel very weak.
—Then why not wash your face? The cool water will surely ________ you. ( )
关于电势和电势能的说法正确的是( )