The correct answer is C) Semi-trailer. Semi-trailers are considered "road vehicles" that can be carried on Ro-Ro (roll-on/roll-off) vessels. Ro-Ro vessels are designed to transport wheeled cargo, such as trucks, trailers, and other vehicles that can be driven on and off the ship. Semi-trailers, which are towed by a truck tractor, meet the definition of a road vehicle and are therefore suitable for transport on Ro-Ro vessels. The other options, A) Train and B) Articulated train, are not considered road vehicles and would not be appropriate for transport on a Ro-Ro vessel. Trains and articulated trains operate on rail systems, not roads, and therefore do not fall under the category of "road vehicles" that can be carried on Ro-Ro vessels.