Answer: The mode of transportation that is characterized by low terminal cost, high line cost, and high route flexibility is shipping by sea.
Sea shipping typically has relatively low terminal costs because the loading and unloading of cargo can be done at large ports with specialized equipment that can handle large volumes of goods efficiently. However, the cost of operating and maintaining a sea vessel can be high, as can the costs associated with navigating complex shipping routes and dealing with weather and other environmental factors.
Sea shipping also offers a high degree of route flexibility, as ships can travel to a wide variety of ports and locations around the world. However, because sea shipping is relatively slow compared to other modes of transportation such as air freight, the line cost (i.e. the cost per unit of distance traveled) can be higher.