用高速钢铣刀切削高温合金,一般采用()切削液。
A.水溶性
B.油类极压
C.硫化乳化油
D.氯化煤油
参考答案:A
设有关系模式:SC(sno,cno,grade),各属性含义依次是学号、课程号、分数。要查询分数低于60分的学生学号,正确的SQL语句是______。
A.SEI,ECT sno FROM SC WH ERE grade BETWEEN O AND 60
B.SELECT sno FROM SC WHERE grade<60
C.SELECT sno FROM SC HAVlNG grade BETWEEN O AND 60
D.SELECT sno FROM SC HAVING grade<60
旁路系统操作时的注意事项有什么?