A:be
B:are
C:do
D:is
运动员掷铅球,铅球在空中的飞行轨迹如图所示,不计空气阻力,下列说法正确的是( )
——Doctor! I can't fall at night.——Don't worry! You are too stressed. Just be relaxed and take some pills, then you'll be better.
How is Mary going to Tibet?
一台理想变压器,原、副线圈的匝数比n1∶n2= 1∶4。原线圈接入220V交流电压,副线圈的电压为( )