Purchase orders are placed with suppliers by:

The correct answer is procurement because this function is specifically responsible for the process of acquiring goods and services necessary for a business's operations. Procurement involves identifying the need for products, selecting suppliers, negotiating terms, and ultimately placing purchase orders with those suppliers. This function ensures that an organization maintains its supply chain effectively and that materials are sourced in a timely and cost-efficient manner.

While other functions have roles related to the supply chain, they do not primarily focus on the purchasing aspect. Warehousing is concerned with storing and managing inventory, customers are the buyers of the end products and do not place orders with suppliers on behalf of the organization, and inventory management focuses on tracking and managing stock levels rather than directly dealing with suppliers for procurement.