Final answer:
To display hidden columns in an SQL table, you must query the database's information schema or equivalent system tables or functions that list table metadata, depending on the database system being used.
Step-by-step explanation:
The question is asking which SQL query would display hidden columns in a PROMOTION table. In SQL, a common method to retrieve all the column names of a table, including hidden ones, would be to query the database's information schema if the database system supports this feature, or to use specific database-engine system tables or functions that provide metadata about the tables.
However, it's important to note that the concept of hidden columns may differ across different database management systems. Oracle, for example, allows columns to be marked as invisible. In these cases, the column data isn't returned in SELECT * statements, but can be retrieved by specifically requesting the column in a SELECT statement. In SQL Server, you might use system views to see all columns. To assist the student, it would be important to know the specific database system in use.