Section: Evidence-Based Reading

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Passage 1 suggests that active volcanoes

1. Are entirely confined to land, and that there are about 500
2. Land-based, with each acting as a potential world ender
3. Sea-based, and necessary for regulating earths temperatures
4. Are land- and sea-based with 500 known on the earth's surface

Answer 4: the author is only willing to give a number on the land-based volcanoes, but he does mention those located in the sea.