According to Mr. Ochoa, what lets rainwater dissolve limestone?
Basic Understanding of Spoken English · TELPAS Grades 8–9 listening. The correct answer, and the reasoning behind it.
Reporting category 2: understand the main points and important details of spoken stories and informational passages, about everyday life and school subjects.
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How Caves Are Made
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Mr. Ochoa: Central Texas is full of caves, and some of them are big enough to walk through. Today I want you to understand how a cave can form inside solid rock. The answer is water, and a lot of time.
Mr. Ochoa: Much of the Hill Country sits on a kind of rock called limestone. When rain falls, it picks up a gas called carbon dioxide from the air and the soil. That turns the rainwater into a very weak acid. It's much too weak to hurt your skin, but limestone slowly dissolves in it.
Mr. Ochoa: The water seeps into tiny cracks in the limestone. Over thousands and thousands of years, it dissolves the rock little by little, and the cracks grow into tunnels and rooms.
Mr. Ochoa: Once a cave fills with air, something else happens. Water dripping from the ceiling leaves behind tiny bits of mineral. Drip by drip, those bits build up into stone icicles called stalactites. Where the drops land on the floor, mounds called stalagmites grow upward. Here's how to remember which is which. Stalactites hold tight to the ceiling. Stalagmites might reach them someday.
The question
Choose the best answer.
According to Mr. Ochoa, what lets rainwater dissolve limestone?
- Rain falls on it very hard.
- The water is heated by warm rock underground.
- Stalactites drip minerals onto it.
- Carbon dioxide turns it into a weak acid.Correct answer
Why “Carbon dioxide turns it into a weak acid.” is correct
This is a detail question about cause and effect. Mr. Ochoa says rain "picks up a gas called carbon dioxide," which "turns the rainwater into a very weak acid," and limestone dissolves in it. Science words like dissolve and acid can make this harder for English learners.
Why the other answers are wrong
- Rain falls on it very hard. — He says the rock dissolves slowly, not that it is broken by force.
- The water is heated by warm rock underground. — The temperature of the water is never mentioned.
- Stalactites drip minerals onto it. — Dripping minerals build stalactites later, after a cave forms.
Practice more of this
More listening practice for Grades 8–9, or see the TELPAS practice test for 8th and 9th grade.
This is an independent study resource. It is not affiliated with, endorsed by, or connected to the Texas Education Agency or the official TELPAS program. All questions here are original practice material written to match the published test design.