9781422270653

WORDS TO UNDERSTAND

allergen: any substance—such as pollen, dust, mold, and pet dander—that is recognized by the immune system and can cause an allergic reaction historical landmarks: buildings or other structures that are protected under law because they have special value due to historical, cultural, or other factors pollutant: any substance (such as tobacco and other types of smoke, household chemicals, etc.) that is introduced into the environment that causes a negative effect on humans, plants, animals, ecosystems, and the overall environment scaffold: a temporary raised structure that tradesworkers use to work at heights that would otherwise be hard to reach sprinkler system: a fire protection structure that typically runs along the ceiling and shoots out water when high heat from a fire is detected union: an organization that seeks to gain better wages, benefits, and working conditions for its members; it is also called a labor union or trade union

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