Explanation:
This statement provides correct syntax to define the FOREIGN KEY constraint on the DEPTNO column of the EMP table.
Incorrect Answers:
1: There is incorrect syntax, because list of columns and column for the constraint need to be surrounded with the brackets.
3: It is incorrect to use FOREIGN KEY keywords to define constraint on the table. It can be used to add integrity constraint to existing table.
4: It is incorrect to use FOREIGN KEY keywords to define constraint on the table. It can be used to add integrity constraint to existing table.
OCP Introduction to Oracle 9i: SQL Exam Guide, Jason Couchman, p. 238-245
Chapter 5: Creating Oracle Database Objects

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