Final answer:
The maximum speed limit for vehicles towing trailers can vary by jurisdiction, but a common speed limit might be around 80 km/h. It is essential to check local traffic regulations for the exact limit.
Step-by-step explanation:
The maximum speed limit for vehicles towing trailers on a two-way undivided highway is not universally set and can vary by jurisdiction. However, of the options provided (40 km/h, 60 km/h, 80 km/h, 100 km/h), a common speed limit for towing vehicles might be around 80 km/h, though it is often lower to ensure safety due to the reduced maneuverability and increased stopping distance of towing vehicles. For a precise and current speed limit, it is important to check the specific traffic regulations of the area in which you are driving.