Step 1: What the question asks.
We need the SQL keyword whose purpose is to combine rows from two tables when a condition is met.
Step 2: Spot the key phrase.
The phrase that meets a condition points to a join condition. Only JOIN works on a condition between two tables.
Step 3: Try an example.
With tables STUDENT(id, name) and RESULT(id, marks), the query SELECT name, marks FROM STUDENT JOIN RESULT ON STUDENT.id = RESULT.id places each name next to its marks. The condition decides which rows are paired.
Step 4: Test the set operators on the same idea.
UNION, INTERSECT and MINUS need both queries to have the same columns. They compare complete rows. None of them pairs rows by a condition.
Step 5: Eliminate.
UNION merges, INTERSECT keeps common rows, MINUS subtracts rows. Only JOIN matches the description.
Step 6: Match with the options.
JOIN is the third printed option.
Step 7: Why each wrong option fails.
UNION only stacks rows of two queries and removes repeats, so it needs no condition. INTERSECT only keeps the rows found in both results. MINUS only keeps rows of the first result that are missing from the second. None of the three looks at a matching condition between two tables, so options 1, 2 and 4 are all wrong.
Final Answer:
The clause is JOIN, option 3.
\[ \boxed{3} \]