The correct option is D It is beneficial during emergencies.
Air transport is one of the fastest modes of travel. Aeroplanes can carry people, mail and lightweight goods to distant places in the shortest time possible. They also prove to be extremely useful during the times of natural calamities, wars and other emergencies. But, they are the most expensive form of travel, which makes them inaccessible to a lot of people in India. It is also a major source of pollution and global warming.