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 CONSTRAINT stud_id_pk PRIMARY KEY student_id;

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

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

D.
ALTER TABLE students
ADD PRIMARY KEY student_id;

E.
ALTER TABLE students
ADD 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
D no such MODIFY keyword
Refer : Introduction to Oracle9i : SQL, Oracle University Study Guide, 10-17