Explanation:
The correct statement to create user is: CREATE USER user_name IDENTIFIED BY password.
Incorrect Answers:
1: This syntax is incorrect to create user: you need to provide also password for the user.
2: There is no CREATE OR REPLACE USER command in Oracle.
3: There is no CREATE NEW USER user_name DEFAULT command in Oracle.
5: There is no CREATE NEW USER user_name IDENTIFIED BY command in Oracle.
6: There is no CREATE OR REPLACE USER user_name IDENTIFIED BY command in Oracle.
OCP Introduction to Oracle 9i: SQL Exam Guide, Jason Couchman, p. 348-351
Chapter 8: User Access in Oracle

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