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4th Grade Chapter 4 Lesson 4 How do people disturb the balance?
substance that is very harmful to humans & other organisms
mining companies must replace rock & soil that were removed
pollutant that can harm the ocean's plants and animals
good indicator of air quality
Water becomes ____________ when wastes & chemicals get into rivers, lakes & oceans.
National Parks System
established by the United States to preserve historic sites & habitats of many plants & animals
world's first national park