The plane must be ready within half an hour. There should be no in sending the blood and medicine to the injured people.A.hurry B.delay C.time D.wait 答案:B13.物理学中常用功率来表示做功的快慢程度,单位时间完成的功叫做功率,写成公式即P=$\frac{W}{t}$,在国际单位制中,功率的单位是W.某机器的功率为5W,其物理意义是1s内做功5J.