A passage states that coral reefs support 25% of all marine species, protect coastlines from storms, generate billions in tourism revenue, and provide food for millions of people. What is the main idea?
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A
Coral reefs are colorful underwater structures
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B
Coral reefs are critically important ecosystems with ecological, protective, economic, and nutritional value
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C
Tourism is the most important benefit of coral reefs
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D
Marine species cannot survive without coral reefs