Final answer:
Pushing down selections in a query can affect the set of tuples produced by the query.
Step-by-step explanation:
The statement is true. Pushing down selections in a query can affect the set of tuples that are produced by the query. When applying selection criteria to a query, the database system filters the data based on the specified conditions. By pushing down selections, the database engine can reduce the amount of data it needs to process, resulting in more efficient and optimized query execution.