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.
Which of the following best expresses the central idea of the passage?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → The Ganga river dolphin lives by sound in muddy water, but a louder, broken-up river makes this harder.
The passage first shows how the dolphin lives by sound, and then shows what is going wrong.
- In muddy water its eyes are “of little use”. It sends out clicks and builds “a picture of the water” from the echoes.
- Then comes “the trouble”. Engine noise makes the echoes come back unclear. Dams and barrages “cut the river into pieces”, and nets trap dolphins.
- The last line puts the dolphin’s clicks and a diesel engine in “the same brown water”. The whole passage leads to this clash.
Why the Other Options are Incorrect?
Option 2: Boatmen know the Ganga river dolphin better than anyone else, since they hear it long before they ever see it. — Incorrect. Wrong focus: The boatman only opens the passage. The writer never says boatmen know the dolphin best.
Option 3: The dolphin sends out clicks and reads their echoes, which tell it where rocks, banks and fish are. — Incorrect. Too narrow: This is only the second paragraph. It leaves out the noise, dams and nets that now make life hard for the dolphin.
Option 4: Naming the dolphin the national aquatic animal has done more to protect it than any other step. — Incorrect. Not mentioned: The passage gives the 2009 naming as a fact only. It says the dolphin is “still listed as endangered”.