A six – digit card field used for postal ZIP codes is defined as

The correct answer is: D. An alphanumeric field.

A six-digit card field used for postal ZIP codes is defined as an alphanumeric field because it can store both letters and numbers. This is because ZIP codes are made up of both letters and numbers, such as 91234.

A letter field is a field that can only store letters. An alphabetic field is a field that can only store letters and numbers. A numeric field is a field that can only store numbers. None of the above is not a valid answer.