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Information and IdeasEasyMain idea of a passage

Information and Ideas practice question

Sea otters eat sea urchins, and sea urchins eat kelp. Along stretches of coast where otters were hunted to near-extinction, urchin numbers exploded and the kelp forests disappeared. Where otters have since returned, the kelp has grown back. The health of an entire underwater forest, it turns out, depends on a single predator.

Which choice best states the main idea of the text?

  1. A. By keeping sea urchin numbers in check, sea otters allow kelp forests to survive.Correct
  2. B. Sea urchins are the most important animals in a kelp forest.
  3. C. Kelp forests can recover without any help from predators.
  4. D. Sea otters were hunted because they ate too much kelp.

Answer: A. By keeping sea urchin numbers in check, sea otters allow kelp forests to survive.

Every sentence builds the same chain: otters control urchins, urchins destroy kelp, so otters protect kelp. The last sentence states it outright — the forest depends on the predator.

Why the other answers are wrong

B. Sea urchins are the most important animals in a kelp forest.
The text presents urchins as the problem that otters solve, not as the key to the forest's health.
C. Kelp forests can recover without any help from predators.
The text says the opposite: kelp vanished without otters and returned with them.
D. Sea otters were hunted because they ate too much kelp.
Otters eat urchins, not kelp, and the text gives no reason for the hunting.

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