The correct option is B
Specific tax
A per unit tax, or specific tax, is a tax that is defined as a fixed amount for each unit of a good or service sold, such as cents per kilogram. It is thus proportional to the particular quantity of a product sold, regardless of its price.
An ad valorem tax is a tax whose amount is based on the value of a transaction or of property. It is typically imposed at the time of a transaction, as in the case of a sales tax or value-added tax