A customer receives a confirmation that discloses the firm has acted in a principal capacity.

When a firm acts in a principal capacity, it trades securities for its own account, buying or selling directly to or from its inventory. The firm’s role differs from an agency capacity, where it acts as an intermediary.

A is correct because principal capacity involves selling directly from the firm's inventory.

B, C, and D are incorrect because these scenarios describe agency transactions, where the firm facilitates trades between two parties.