Answer:
Proportion of sales of each department.
Step-by-step explanation:
Advertising expense directly effects the sales of the business. As the campaign is made store-wide sales and it does not directly traceable to any specific department. It need proper basis for allocation of expenses. The proportion of sales of each department is the most suitable basis from all of the given options because the share of benefit from the campaign is received in the form of sale. A campaign might mostly effects the sales.