The correct answer is D.
An ad-valorem tax is a tax in which the amount due depends on the value of an item exchanged in a transaction or on the value of an underlying property.
The most representative example is the valued-added tax (VAT), in which the amount due is a percentage of the total value of the good purchased and it is paid simultaneosly when the good is bought. A property tax is also ad-valorem but needs to be paid periodically, for instance, anually.