根据SQL标准,增加一个新的字段sdate到表student中,该字段为可容纳7个字符的定长字符串,下面哪
A insert into student sdate char(7)
B add sdate char(7) to student
C append sdate varchar(7) to table student
D alter table student add sdate varchar(7)
E alter table student add sdate char(7)
F alter table student modify sdate char(7)