A、ALTER TABLE student_grades   ADD   FOREIGN KEY (student_id) REFERENCES students(student_id);
B、ALTER TABLE student_grades   ADD CONSTRAINT NAME = student_id_fk   FOREIGN KEY (student_id) REFERENCES students(student_id);
C、ALTER TABLE student_grades   ADD CONSTRAINT student_id_fk   FOREIGN KEY (student_id) REFERENCES students(student_id);
D、ALTER TABLE student grades   ADD NAMED CONSTRAINT student_id_fk   FOREIGN KEY (student_id) REFERENCES students(student_id);
E、ALTER TABLE student grades   ADD NAME student_id_fk   FOREIGN KEY (student_id) REFERENCES students(student_id);