Which statement accomplishes this task?

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 student_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);

Explanation:
ALTER TABLE table_name
ADD [CONSTRAINT constraint] type (coloumn);
Incorrect answer:
A:
wrong syntax
B:
wrong syntax
C:
wrong syntax
E:
no such MODIFY keyword
Refer: Introduction to Oracle9i: SQL, Oracle University Study Guide, 10-17