根据向执行元件的供油方式,下面选项中不属于这种的方式的是:()
A.串联系统
B.并联系统
C.开式循环系统
参考答案:C
已知关系模式:sc(sno,sname,grade),各属性含义依次为学号、课程名、分数。要查找“数据库”课分数最高的学生的学号,正确的SQL语句是
A.SELECT sno FROM sc WHERE sname = "数据库" AND grade = MAX(grade)
B.SELECT sno FROM sc FOR sname = "数据库" OR grade>=MAX(grade)
C.SELECT sno FROM sc WHERE sname = "数据库" AND grade = (SELECT MAX(grade) FROM sc)
D.SELECT sno FROM sc FOR sname = "数据库" OR grade = (SELECT MAX(grade) FROM sc)
日常生活垃圾和污物应怎样处理?