The keyword used with UNION that retains duplicate rows is . . . . . . . .

This question is about the UNION operator in MySQL. The UNION operator combines the result sets of two or more SELECT statements.

The keyword ALL is used with the UNION operator to retain duplicate rows. This means that if a row appears multiple times in either of the SELECT statements, it will be included in the final result set multiple times.

Option A: ALL is the correct answer.

Option B: NARROW, Option C: STRICT, and Option D: DISTINCT are incorrect.

DISTINCT is used to remove duplicate rows from the result set.