What did you do yesterday? ____.
A:I am doing my homework.
B:I played basketball.
C:I am a pupil.
“有心栽花花不开,无心插柳柳成荫”,“插柳”采取的方法是( )
(不计绳重与摩擦,且动滑轮重G动小于物重G),用它们分别将重相同的甲、乙两物体匀速提升相同的高度,所用的拉力分别为F甲、F乙,它们的机械效率分别为η甲、η乙。则下列关系正确的是:( )