The correct answer is: D. Primary key
A primary key is a field or combination of fields that uniquely identifies each record in a table. It is used to enforce referential integrity and to make queries more efficient.
An AutoNumber field is a field that automatically generates a unique number for each record that is added to the table. It is not a primary key, because it is not guaranteed to be unique.
An index field is a field that is used to speed up queries. It is not a primary key, because it does not uniquely identify each record in the table.
Field order is the order in which the fields are displayed in the table. It does not determine the sort order of the table.
Here is a more detailed explanation of each option:
- AutoNumber field
An AutoNumber field is a field that automatically generates a unique number for each record that is added to the table. It is not a primary key, because it is not guaranteed to be unique. For example, if two records are added to the table at the same time, they could both have the same AutoNumber value.
- Index field
An index field is a field that is used to speed up queries. It is not a primary key, because it does not uniquely identify each record in the table. For example, you could create an index on the LastName field in a table of customers. This would make it faster to find all customers with the last name “Smith”.
- Field order
Field order is the order in which the fields are displayed in the table. It does not determine the sort order of the table. For example, if you have a table with the fields FirstName, LastName, and Email, you could display the fields in any order you want. The sort order of the table would still be determined by the primary key.
- Primary key
The primary key is a field or combination of fields that uniquely identifies each record in a table. It is used to enforce referential integrity and to make queries more efficient. For example, if you have a table of customers, the primary key could be the CustomerID field. This would ensure that each customer has a unique ID number.