Concept:Water transport is known for its low cost and very slow speed over long distances.
Explanation:Among the given options, water transport carries heavy goods at the lowest cost per tonne.
It uses rivers, seas, and oceans, where no expensive roads or tracks are built.
However, its speed is very slow compared with rail, air, or pipeline transport.
Air transport is the fastest and most expensive.
Rail transport is faster than water but more expensive for bulk goods.
Pipeline transport is efficient only for liquids or gases and does not move general cargo.
Therefore, water is the slowest and cheapest general means of transport listed.
Answer:B. Water