Numerical answer
Five sentences related to a topic are given below. Four of them can be put together to form a coherent, meaningful and unified paragraph. Identify the sentence that does not fit and key in its number as your answer.
1. Coral reefs, though they occupy less than one percent of the ocean floor, are home to roughly a quarter of all known marine species.
2. This extraordinary biodiversity depends on a fragile symbiosis between coral polyps and microscopic algae living within their tissues, which supply the coral with most of its energy.
3. When ocean temperatures rise even slightly above normal for a sustained period, corals expel these algae in a stress response known as bleaching, often leading to widespread coral death.
4. Overfishing in tropical coastal economies has pushed several commercially valuable fish species toward the brink of collapse in recent decades.
5. Because reef recovery after a severe bleaching event can take a decade or more, repeated bleaching episodes in quick succession leave little time for reefs to rebuild before the next stress event arrives.
1. Coral reefs, though they occupy less than one percent of the ocean floor, are home to roughly a quarter of all known marine species.
2. This extraordinary biodiversity depends on a fragile symbiosis between coral polyps and microscopic algae living within their tissues, which supply the coral with most of its energy.
3. When ocean temperatures rise even slightly above normal for a sustained period, corals expel these algae in a stress response known as bleaching, often leading to widespread coral death.
4. Overfishing in tropical coastal economies has pushed several commercially valuable fish species toward the brink of collapse in recent decades.
5. Because reef recovery after a severe bleaching event can take a decade or more, repeated bleaching episodes in quick succession leave little time for reefs to rebuild before the next stress event arrives.
Show answer and solution
Answer: 4
Sentences 1, 2, 3 and 5 trace one continuous thread: coral reefs' biodiversity (1), the algal symbiosis underlying it (2), how heat stress disrupts that symbiosis through bleaching (3), and the long recovery time that repeated bleaching threatens (5). Sentence 4, about overfishing of commercial fish species, introduces an unrelated threat to tropical fisheries rather than continuing the coral-bleaching thread. The odd one out is sentence 4.
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