Final answer:
None of the options provided (a, b, or c) is necessarily equivalent to the cross join query without additional information about the structure of the involved tables.
Step-by-step explanation:
The determining which of the provided SQL queries is equivalent to the given query: SELECT title, gift FROM books CROSS JOIN promotion. The cross join combines all rows from the first table with all rows from the second table, which results in a Cartesian product of the two tables. The correct answer is: a. SELECT title, gift FROM books NATURAL JOIN promotion; Natural join performs a join based on the common columns between two tables. However, it would only work if both the books and promotion tables have precisely the columns named 'title' and 'gift'. As we don't have that information, we cannot confirm this is equivalent without knowing the table structure.
b. SELECT title FROM books INTERSECT SELECT gift FROM promotion; The INTERSECT operator returns the common values between two datasets. This doesn't produce a Cartesian product and is not equivalent. c. SELECT title FROM books UNION ALL SELECT gift FROM promotion; The UNION ALL operator combines the results of two or more SELECT statements into a single set, including duplicates. It also does not represent a Cartesian product and is therefore not equivalent. Conclusion: None of the options (a, b, or c) is necessarily equivalent to the original cross join query without additional information about the table structures.