You need to modify the STUDENTS table to add a primary key on the STUDENT_ID column. The table is currently empty.Which statement accomplishes this task?（）

A.ALTER TABLE students ADD PRIMARY KEY _ id;

B.ALTER TABLE students ADD CONSTRAINT PRIMARY KEY (student_id);

C.ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY student_id;

D.ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY (student_id);

E.ALTER TABLE students MODIFY CONSTRAINT stud_id_pk PRIMARY KEY (student_id);