<span>A. genetic variation in species
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When we exercise, we are burning body fat. During exercises, the quantity of body fat cells will start to decrease. As a result, a dominant percentage of the fat molecules are exhaled as carbon dioxide.
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The primary reason that fossil fuels are harmful to the environment is that their use produces large amounts of greenhouse gasses. These gasses cause heat to build up in the atmosphere and raise the average temperature of the planet. Fossil fuels also pollute the air when they're burned and may cause environmental damage when they're mined
