题型:选择题 I will not wait for him for a second-he may have something else to do, so he could not__________here.[ ]A. come up B. come outC. turn out D. turn up 查看答案
题型:单项选择题 离心泵出口单向阀的作用()。A.防止泵的出口液体倒流,避免事态扩大B.防止液体倒流使叶轮倒转,叶轮倒转会使叶轮备帽脱落产生事故C.防止泵出口液体倒流进入吸入口产生超压D.防止离心泵停车以后,出口物料倒流到吸入口而浪费能源 查看答案