用撬棍撬石头,已知动力臂是阻力臂的5倍,若石头作用在棍上的阻力为500N,则所需的动力至少为______N.
动力=阻力×阻力臂动力臂=500N5=100N
故答案:100.
慢性肾衰竭急性发作与急性肾衰竭比较,重要的差别是()
A.水肿、少尿、血尿
B.氮质血症
C.代谢性酸中毒
D.生长发育落后、明显贫血和肾性骨病
E.电解质紊乱
The book, which is a useful guide for today's young people, deals with many questions and problems that face them at school and at home as well as in society.
A.are faced
B.confront
C.in opposition
D.meet