Final answer:
To display a unique list of automobile makes that have never been rented using a left outer join, you can write and execute a query.
Step-by-step explanation:
In order to display a unique list of automobile makes that have never been rented using a left outer join, you would need two tables: one for the automobiles and one for the rentals. To display a unique list of automobile makes that have never been rented using a left outer join, you can write and execute a query. Let's assume the automobile table has a column 'make' and the rentals table has a column 'make' as well. You can write and execute the following query:
SELECT DISTINCT automobile.make FROM automobile LEFT OUTER JOIN rentals ON automobile.make = rentals.make WHERE rentals.make IS NULL;
This query will return a list of automobile makes that are present in the automobile table but not in the rentals table.