The most useful allocation basis for the departmental costs of an advertising campaign for a storewide sale is likely to be:

A) Floor space of each department.
B) Relative number of items each department had on sale.
C) Number of customers to enter each department.
D) An equal amount of cost for each department.
E) Proportion of sales of each department.

The proportion of sales of each department is the most appropriate allocation basis for the departmental costs of an advertising campaign for a storewide sale because it directly links the costs to the revenue generated by each department. This method ensures that the departments which benefit the most from the advertising campaign contribute more towards the campaign’s cost. It also incentivizes departments to increase their sales, which ultimately benefits the overall profitability of the company.