Numerical answer
Five sentences related to a common theme are given below. Four of them can be logically ordered to form a coherent paragraph, while one does not fit. Identify the sentence that does not belong.
1. Lighthouses once required a live keeper because the light source, typically an oil lamp, needed constant tending to stay lit through the night.
2. Automation arrived gradually across the twentieth century, first through clockwork mechanisms that rotated the lens without human help, and later through electric lamps that rarely failed.
3. Many lighthouse keepers kept detailed logbooks describing passing ships, an unintentional archive that maritime historians now consult for shipping records long since lost elsewhere.
4. By the 1990s, most of the world's remaining lighthouses had been converted to fully automated, remotely monitored operation, ending a profession that had existed for over two centuries.
5. The keeper's role, once essential, was rendered redundant by the same reliability improvements that had originally justified building lighthouses in the first place.
1. Lighthouses once required a live keeper because the light source, typically an oil lamp, needed constant tending to stay lit through the night.
2. Automation arrived gradually across the twentieth century, first through clockwork mechanisms that rotated the lens without human help, and later through electric lamps that rarely failed.
3. Many lighthouse keepers kept detailed logbooks describing passing ships, an unintentional archive that maritime historians now consult for shipping records long since lost elsewhere.
4. By the 1990s, most of the world's remaining lighthouses had been converted to fully automated, remotely monitored operation, ending a profession that had existed for over two centuries.
5. The keeper's role, once essential, was rendered redundant by the same reliability improvements that had originally justified building lighthouses in the first place.
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Answer: 3
Sentences 1, 2, 4 and 5 trace one continuous narrative: why keepers were needed, how automation arrived, when it was completed, and why the role became redundant. Sentence 3, about keepers' logbooks as historical archives, is a genuinely interesting but tangential fact about keepers that does not belong to this narrative of automation — it neither sets up nor follows from the surrounding sentences' logic. Answer: 3.
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