Read the passage and answer the questions given below it.
A boatman on the Ganga will tell you that you hear the river dolphin before you see it. It comes up for air with a short puff, and that sound is why people along the river call it the susu. Then it slips back into water the colour of milky tea.
In water that muddy, eyes are of little use, and this dolphin has almost given up on them. Its eyes are tiny and have no lens. They can tell light from dark, and not much more. The animal finds its way by sound instead. It sends out a stream of clicks and listens for the echoes that bounce back from rocks, banks, fish and the river bottom. From these echoes it builds a picture of the water around it. Scientists call this echolocation. It also has an odd habit: it often swims on its side.
This way of living served it well for a very long time, in the Ganga, the Brahmaputra and the rivers that feed them. The trouble is that the river has grown loud. Motorboats and ferries fill the water with the hum of engines, and the echoes the dolphin depends on come back muffled. Dams and barrages cut the river into pieces. Nets put out for fish trap dolphins too.
In 2009 India named the Ganga river dolphin its national aquatic animal. It is still listed as endangered. On a busy morning near a ferry ghat, the clicks of a susu and the drone of a diesel engine travel through the same brown water.
It can be inferred from the passage that the dolphin’s poor eyesight
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → matters little where it lives, since sound does the work of sight.
The dolphin cannot see well, but this does not hold it back in its own river.
- The passage says that “in water that muddy, eyes are of little use”. Even good eyes would not see much there.
- The dolphin “finds its way by sound instead”. Its clicks and their echoes show it rocks, banks and fish.
- The writer adds that this way of living “served it well for a very long time”. So weak eyes are not a real problem for it.
Why the Other Options are Incorrect?
Option 1: was caused by the growing noise of boats and engines on the river. — Incorrect. Wrong link: In the passage, engine noise spoils the echoes the dolphin hears. It has nothing to do with its eyes.
Option 2: is the main reason that the dolphin gets caught in fishing nets. — Incorrect. Not mentioned: The passage only says that nets put out for fish trap dolphins too. It gives no reason linked to eyesight.
Option 4: is a recent change brought on by the river becoming muddier. — Incorrect. Contradicted: The passage says the dolphin has lived this way “for a very long time”. It is not a new change.