approach should you recommend?

You are designing a SharePoint 2010 solution that allows users to enter address information for contacts into a
list named Address. You have the following requirements:
Ensure that users enter full nine-digit zip codes for the address information.

.Display a custom message indicating that a zip code is invalid if the entered zip code does not match the full
nine-digit requirements. You need to ensure that the application is designed to meet these requirements. Which
approach should you recommend?

A.
Create a custom command.

B.
Create a Datasheet view on the Address list.

C.
Use the Form Options of the Address list.

D.
Create a formula on the column.