在 scores 表 sno 列上添加参照student表sno列的外键约束,正确的 SQL 语句是()
A.
alter table scores add constraint fk_cno foreign key ( sno ) references student ( sno )
B.
alter table scores add constraint fk_cno foreign key ( sno )
C.
alter table scores add foreign key ( sno ) references student ( sno )
D.
alter table scores add constraint foreign key ( sno )