SQL的DROP INDEX语句的作用是______。

A．服务攻击
B．非服务攻击
C．对象攻击
D．非对象攻击

A．和所在系(SD)，实现该功能的正确SQL语句是______。A) SELECT XM, SA, SD FROM STUD
WHERE BETWEEN 20＜SA＜23;
B．SELECT XM, SA, SD FROM STUD
WHERE SA BETWEEN 23 AND 20;
C．SELECT XM, SA, SD FROM STUD
WHERE SA NOT BETWEEN 20 AND 23;
D．SELECT XM, SA, SD FROM STUD
WHERE SA BETWEEN 20 AND 23;