A:U2=U1,E2=E1
B:U2=2U1,E2=4E1
C:U2=U1,E2=2E1
D:U2=2U1,E2=2E1
—Lisa, is this your shoe?
—Yes, it is. But where is _______?
关于曲线运动的速度,下列说法正确的是( )
This is Mr White's ________ trip to Beijing. He has been there twice before.