Read the following passage:
An increase in automobile use has led to increased
demand for fuel. The extraction, processing, and delivery
of fuel put harmful pollutants into the atmosphere. The
fuel that is then consumed by engines creates carbon
dioxide emissions. The carbon dioxide creates a
greenhouse effect in the atmosphere. The gasses trap
heat in Earth's atmosphere, leading to global warming.
Which statement best describes the main idea of this passage?
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A. Life was better before the invention of automobiles.
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B. Most people are unaware of how air pollution affects the
environment.
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C. Mass transit creates less air pollution than individual automobiles.
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D. People should reduce their use of automobiles or drive cleaner
vehicles.