在下表中查询员工人数大于1人的部门以及该部门的平均绩效成绩
表名: 绩效成绩
A. select 部门, avg(成绩) from 绩效成绩 where 员工id > 1
B. select 部门, avg(成绩) from 绩效成绩
group by 部门
having 员工id > 1
C. select 部门, avg(成绩) from 绩效成绩
group by 部门
having count(员工id) > 1
D. select 部门, avg(成绩) from 绩效成绩
where count(员工id) > 1
group by 部门