Concept:The statement describes the mode of transport that is slow, inexpensive, and suitable for moving heavy cargo across countries.
Explanation:Sea transport moves goods using ships and ocean routes.
It is slower than road, rail, and air transport because ships travel at lower speeds over long distances.
However, ships have a very large carrying capacity.
This makes them ideal for transporting bulky goods such as oil, grains, coal, and machinery.
The cost per tonne for sea transport is lower than other international modes.
Therefore, it is the cheapest option for long-distance trade between nations.
Among the given options, road, rail, and air do not match all these features.
Only sea transport fits the description.
Answer:D. sea transport