How can the app builder satisfy this requirement?

The app builder at Universal Containers has been asked to ensure that the Country field on the Account object is captured as the two-letter abbreviation.

How can the app builder satisfy this requirement?
A . Create a validation rule to set values using an external data source.
B . Create a workflow rule that only allows the expected format.
C . Create a validation rule that only allows the expected format.
D . Create a workflow rule to set values using an external data source.

Answer: C