The correct answer is: A selling and distribution cost.

As the deliveries will only occur when a sale has been made it is therefore a selling and distribution cost.

Prime cost is the name given to the total of all the direct production costs, not a cost incurred when distributing goods after they have been sold.

Production overheads are the costs incurred in making goods which cannot be identified directly to the goods made by the company, not a cost incurred when distributing goods after they have been sold.

A direct production expense is incorrect. These are the expenses other than materials and labour costs which are incurred in full as a direct consequence of making the product, not a cost incurred when distributing goods after they have been sold.