MySQL实现高可用可以借助下面的哪个工具实现（）

A.insert into student(sal) values（8000）;
B.select sun(age)from students;
C.delete from student where id=3;
D.select max(age) from students;

A.add
B.at
C.like
D.as

A.alter table score drop id;
B.alter table score delete id;
C.alter table score modify id;
D.alter table score change id;