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?（）

AALTER TABLE students ADD PRIMARY KEY student_id;

BALTER TABLE students ADD CONSTRAINT PRIMARY KEY (student_id);

CALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY student_id;

DALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY (student_id);

EALTER TABLE students MODIFY CONSTRAINT stud_id_pk PRIMARY KEY (student_id);