Answer:
Create a validation rule
Explanation:
Solution
The action a developer would take to enforce this requirement is by creating a validation rule.
Validation rule: A validation rules demonstrate that the data a user enters in a record meets the standards you identify before the user can save the record.
A validation rule can have a formula or expression that assesses the data in more than one fields and returns a value of either “True” or “False”.
It allow for values which are or are not allowed on a specific field.
