To understand these SQL statements, the user needs to know the basic syntax of the SELECT statement and the ORDER BY clause. The SELECT statement retrieves data from one or more tables, and the ORDER BY clause sorts the results in ascending or descending order based on one or more columns' values.

The first SQL statement retrieves the last_name, salary, and hire_date columns from the EMPLOYEES table and sorts the results in descending order based on the salary column's values.

The second SQL statement retrieves the last_name, salary, and hire_date columns from the EMPLOYEES table and sorts the results in descending order based on the second column, which is the salary column.

A. The two statements produce identical results. This is correct because both statements retrieve the same columns and sort the results in descending order based on the salary column's values.

B. The second statement returns a syntax error. This is incorrect because the second SQL statement is syntactically correct and will execute without errors.

C. There is no need to specify DESC because the results are sorted in descending order by default. This is incorrect because the default order is ascending, not descending. If the user wants to sort the results in descending order, they must specify DESC explicitly.

D. The two statements can be made to produce identical results by adding a column alias for the salary column in the second SQL statement. This is incorrect because adding a column alias does not affect the sorting order. The two statements already produce identical results, so there is no need to modify them.

Therefore, the answer is: A. The two statements produce identical results.