The correct answer is: A. Referential integrity is enforced.
Referential integrity is a database constraint that ensures that the data in one table is consistent with the data in another table. For example, if a table has a column that references a primary key in another table, referential integrity will prevent you from adding a row to the first table that has a value in the referenced column that does not exist in the second table.
The appearance of symbols, such as 1 and the infinity symbol, at the endpoints of a relationship line in the relationships window indicates that referential integrity is enforced for that relationship. The 1 symbol indicates that the relationship is one-to-one, while the infinity symbol indicates that the relationship is one-to-many.
An inner join is a type of join that returns all rows from the left table that have matching rows in the right table. An outer join is a type of join that returns all rows from both tables, even if there are no matching rows.
I hope this helps!