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Information and IdeasEasy–MediumLocating a stated mechanism

Information and Ideas practice question

Ancient Roman harbour concrete grows stronger in seawater. The water reacts with volcanic ash in the mixture to form new crystals, which fill cracks as fast as they open. Modern concrete, made with different ingredients, simply cracks and crumbles.

According to the text, why does Roman concrete grow stronger in seawater?

  1. A. Seawater reacts with volcanic ash in the concrete to form crystals that fill cracks.Correct
  2. B. Roman concrete never develops cracks.
  3. C. It is made with the same ingredients as modern concrete.
  4. D. It was poured underwater.

Answer: A. Seawater reacts with volcanic ash in the concrete to form crystals that fill cracks.

The text gives the mechanism directly: the reaction with volcanic ash forms crack-filling crystals.

Why the other answers are wrong

B. Roman concrete never develops cracks.
Cracks do open; the crystals fill them.
C. It is made with the same ingredients as modern concrete.
The text says modern concrete uses DIFFERENT ingredients.
D. It was poured underwater.
Nothing is said about how it was poured.

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