When is it mandatory to use reflective triangles or flares?

Answer: B — When stopped on the highway posing a hazard

The requirement to use reflective triangles or flares is primarily intended to enhance safety when a vehicle is stopped on the highway and poses a hazard to other road users. This practice is crucial because it helps to alert approaching drivers of a potential danger, reducing the risk of collisions. When a vehicle is disabled or breaks down, it is often in a location where it may not be immediately visible or where other drivers may not expect a stopped vehicle. Using these warning devices effectively communicates to other drivers that they should proceed with caution. Reflective triangles and flares are especially important on highways where vehicles travel at high speeds, and visibility can be limited. They serve as a critical safety measure not only for the driver of the stationary vehicle but also for other motorists navigating the same roadway. The other options do not capture the essence of when these devices are necessary. For instance, using them during heavy rain might be beneficial for visibility, but it does not constitute a mandatory requirement. Similarly, using them at all times while driving or only during the night does not align with regulations, as there are specific circumstances when their use is legally required. Thus, the correct understanding revolves around their use specifically when stopped on the highway and posing a hazard.