A customer uses a price book to populate list prices.

Comprehensive and Detailed Explanation From Exact Extract:

In Salesforce Pricing (Revenue Cloud):

List Price is typically derived from the price book entry.

A formula-based pricing element can override the list price based on conditions (such as a custom “Emerging Market” flag on the quote).

Downstream pricing steps (discounts, totals, net prices) use this adjusted list price as the base.

Option A matches the documented pattern: override the list price using a formula element.

Option B confuses unit price vs list price as the base.

Option C puts the override into a custom field, which then would require additional custom logic for subsequent pricing steps.