Which allocation base is best used to allocate advertising expense by selling department?

A) Square feet of spaced used
B) Gross sales of each department as a percent of total gross sales
C) An even split among all selling departments
D) Some other method not listed

Gross sales of each department as a percent of total gross sales is the best method to allocate advertising expense by selling department because it directly relates the benefit received from advertising to the sales generated, ensuring a fair and proportional allocation of costs.