What safety equipment must be on board for a commercial vehicle?

The correct answer includes a fire extinguisher, reflective triangles, and spare fuses, which are all crucial components of safety equipment required to be on board a commercial vehicle.

A fire extinguisher is vital for quickly addressing any small fires that may occur, thereby preventing them from escalating into larger emergencies. Reflective triangles are essential for warning other drivers of a roadside emergency, aiding in the visibility of the vehicle to prevent collisions. Spare fuses ensure that electrical systems can be maintained in the event of a failure, allowing the driver to address minor electrical issues on the road.

The other options include items that may be useful but do not encompass all the essential requirements. For instance, while warning lights are critical for safety, the requirement specifically outlines the need for reflective triangles, thus making their absence a deciding factor. Similarly, while reflective vests enhance visibility for drivers outside of their vehicles, they are not categorized as mandatory safety equipment in the same context as the elements included in the correct answer. Emergency signals, while important, do not provide the comprehensive safety coverage that the correct set does.