Concept:Rail transport is the most economical mode for moving bulky goods over long distances.
Explanation:Railways can carry large volumes of cargo in a single trip.
This reduces the cost per unit of goods compared to other transport modes.
Road transport carries smaller loads and becomes more expensive for long-distance bulk movement.
Air transport is very fast but also very costly for heavy goods.
Pipelines are limited to specific liquids or gases, not general bulky goods.
Therefore, rail is the cheapest and most suitable option for bulky goods over long distances.
Answer:A. rail