Answer:
Cost of sales is a product cost since it is directly associated to the production of services by Amazon.
Explanation:
Another term for cost of sales is cost of goods sold. Even though Amazon provides services, it doesn't manufacture any goods, its cost of sales (or COGS) is directly related to the providing of the sales service.
Period costs are not directly associated to the production of goods or services, instead they are incurred as time passes, e.g. rent or interests.