Look! They ____ ____ ____ happily on the playground.
用一个动滑轮在5s内将一重为240N的物体匀速向上提起3m,拉力为150N,求:
— Shall I give you a ride as you live so far away?
— Thank you._________
生活中的一些问题常涉及到化学知识,则下列叙述不正确的是( )