Explanation:
This statement provides correct syntax to add a foreign key constraint to the existing table.
Incorrect Answers:
1: The ADD FOREIGN KEY is wrong construction to add a foreign key constraint to the existing table.
2: The ADD CONSTRAINT NAME is wrong construction to add a foreign key constraint to the existing table.
4: The ADD NAMED CONSTRAINT is wrong construction to add a foreign key constraint to the existing table.
5: The ADD NAME is wrong construction to add a foreign key constraint to the existing table.
OCP Introduction to Oracle 9i: SQL Exam Guide, Jason Couchman, p. 238-239
Chapter 5: Creating Oracle Database Objects

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