* A: Incorrect because the CROSS JOIN of the BRICKS table with itself will produce more than one row.
* B: Incorrect because CROSS JOINing a table with four rows with itself produces 16 rows, but the WHERE condition filters these down.
* C: Incorrect because while a CROSS JOIN of a table with four rows with itself produces 16 rows, this answer does not take into account the WHERE condition.
* D: Correct. The CROSS JOIN will result in 16 combinations (4x4), but the WHERE condition b1.weight < b2.weight will only be true for combinations where the second weight is greater than the first. Since there are 4 distinct weights, there are (42)=6(24)=6 combinations where one weight is less than the other.
* E: Incorrect because this does not account for the conditions specified in the WHERE clause.
* F: Incorrect because the query will return some rows due to the condition specified.