The correct options are
A They are economical and require less maintenance.
B They are useful during natural calamities, especially in conducting relief operations.
C Perhaps play the most important role in facilitating foreign trade.
Water transport is the cheapest and the oldest mode of transport. It does not require huge capital investment in the construction and maintenance, except in the case of canals. The cost of operation of water transport is also very less. Thus, it is a very economical form of transport. It has the largest carrying capacity and is most suitable for carrying heavy goods over long distances. It has played a very significant role in bringing different parts of the world closer and is indispensable to foreign trade. However, waterways are a much slower form of transport when compared to roadways and airways.