存在两个关系teacher(tno,tname,sdept,title)其中tno教师编号,tname教师姓名,sdept所在院系,title职称Course(cno,cname,tno)其中cno课程编号,cname课程名,tno任课教师编号查询职称是讲师或者副教授的老师的姓名和职称。( ) A. select tname,title from teacher where title='副教授' UNIONselect tname,title from teacher where title='讲师' B. select tname,title from teacher where title='副教授' or title='讲师' C. select tname,title from teacher where title='副教授' and title='讲师' D. select tname,title from teacher where title='副教授' ANDselect tname,title from teacher where title='讲师'