查询平均成绩良好， 也就是≥80 分的考生人数， 查询语句就可以写成____。 A: SELECT COUNT(*) FROM (SELECT eeid,avg(achieve) FROM eeexam GROUP BY eeid) AS avgach (eeid,avgachieve)WHERE avgachieve>=80; B: SELECT COUNT(*)FROM (SELECT eeid,avg(achieve)FROM eeexamGROUP BY eeid) avgach (eeid,avgachieve)WHERE avgachieve>=80; C: SELECT dname,(SELECT COUNT(*)FROM examinerWHERE department.dname = examiner.erdepa)FROM departmentWHERE avgachieve>=80; D: SELECT *FROM erexam NATURAL LEFT OUTER JOIN exampaper;