What must an operator display when their load extends more than four feet beyond the rear of the vehicle?

Answer: B — red flag not less than 12 inches in length and width

When a load extends more than four feet beyond the rear of a vehicle, it is crucial for safety that proper warning measures are taken to alert other drivers. The requirement to display a red flag that is not less than 12 inches in length and width serves a clear purpose: it enhances visibility and makes it easier for other road users to gauge the length of the extended load. This is especially critical during daytime and in good weather since a brightly colored flag stands out against most backgrounds. The usage of a red flag is a recognized standard for indicating an extended load because it can be easily seen from a distance. This proactive measure helps prevent accidents and ensures that other drivers are aware of a potentially hazardous situation. Displaying a flag helps maintain safety on the roads by clearly signaling to other drivers that there is a longer-than-normal vehicle or load ahead of them. A warning sign, reflective tape, or a lighted sign are useful in certain situations, but the specific requirement of a red flag is directly aimed at alerting drivers to the physical dimensions of the load, making it the most effective choice in this scenario.