题目：假定student表中有字段grade，grade代表分数，依次统计grade字段的最大值，最小值，平均值的SQL语句是：
A. SELECT max(grade),min(grade),average(grade) FROM student;
B. SELECT max(grade),min(grade),avg(grade) FROM student;
C. SELECT min(grade),average(grade),max(grade) FROM student;
D. SELECT min(grade),avg(grade),max(grade) FROM student;
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