以下MySQL语句中,已知关系模式stu_course(Sno,Cno,Term,Grade),查询成绩良好的人数记录,正确的是( )。 A. SELECT COUNT(grade) AS 成绩良好的人数 FROM stu_course WHERE grade BETWEEN 80 AND 89; B. SELECT COUNT(*) FROM stu_course WHERE grade BETWEEN 80 AND 89; C. SELECT grade AS 成绩良好的人数 FROM stu_course WHERE grade BETWEEN 80 AND 89; D. SELECT * AS 成绩良好的人数 FROM stu_course;