The correct answer is: A. Through train.
A through train is a train that travels from one destination to another without stopping at intermediate stations. ISMD loads are large and heavy, and they require special handling and equipment to move them safely. Through trains are the best way to move ISMD loads because they can travel long distances without stopping, which minimizes the risk of damage or delays.
Shunting trains are trains that are used to move cars around a rail yard. They are not designed to carry large or heavy loads, and they would not be able to safely move ISMD loads. Work trains are trains that are used to perform maintenance on the railway. They are also not designed to carry large or heavy loads, and they would not be able to safely move ISMD loads.
Therefore, the only option that is suitable for moving ISMD loads is through trains.