Final answer:
Operational orders at the company level and below are often issued orally with the aid of a sand table or terrain model, as it provides a hands-on and interactive representation of the terrain.
Step-by-step explanation:
At the company level and below, operational orders (op orders) are most commonly issued orally with the aid of a D) Sand table or terrain model. This visual tool allows for a tangible representation of the terrain to facilitate understanding and discussion among troops. The use of a terrain model helps in conveying complex information effectively, which is critical during operational planning and execution. It serves as a reference for spatial relationships and topographical features key to mission planning. While other options like written memorandums, field manuals, and PowerPoint presentations also have their place in military communications, a sand table or terrain model provides a hands-on and interactive means that can enhance comprehension of the operation's details.