What should an app builder recommend to meet this requirement?

Universal containers wants to ensure that they are accepting clean data from their users and verify that important fields are entered.

What should an app builder recommend to meet this requirement?
A . Update the important fields to be required on the page layout
B. Make a formula field to check the format of the important fields
C. Create a workflow rule to check the fields are formatted correctly
D. Configure a validation to require a field for a specific record type

Answer: D