查询学号为201215121的同学选修过的所有课程的名字，不正确的查询语句是： A: SELECT CnameFROM CourseLEFT JOIN SCON Course.Cno = SCnoWHERE Sno = '201215121'; B: SELECT CnameFROM CourseWHERE Cno IN (SELECT CnoFROM SCWHERE Sno = '201215121'); C: SELECT CnameFROM CourseWHERE EXISTS (SELECT *FROM SCWHERE SCno = Course.CnoAND Sno = '201215121'); D: SELECT CnameFROM CourseWHERE NOT EXISTS (SELECT *FROM SCWHERE SCno = Course.CnoAND Sno = '201215121');