1) fossil fuel include the following except a) coal b) petroleum c) helium gas d) natural gas 2) humans burn fossil fuels to  a) move vehicles b) cut trees c) generate electricity d) move vehicles and generate electricity 3) taking in oxygen and removing CO2 is  a) burning fossil fuels  b) photosynthesis c) respiration 4) co2 levels can -----------increase by volcanic eruptions  a) naturally b) indirectly c) unnaturally 5) when dead animals and plants are broken down a) respiration b) decomposition c) photosynthesis d) burning fossil fuel

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