Correct Answer: DTo create a field on an Opportunity that captures and retains the billing state from its associated Account at the time of the Opportunity's creation, a Flow is the recommended solution. A Formula field would dynamically update based on the Account's current state, which does not meet the requirement for the field to remain static. Roll-up summary fields are used to summarize data from child records, not to capture a snapshot of parent record fields. Apex could be used but often adds unnecessary complexity if simpler configuration options are available. Using a Flow allows for the value to be copied and retained without further updates, meeting the stated requirements effectively.