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