The greenhouse effect is the rise in temperature that the Earth experiences because certain gases in the atmosphere (water vapor, carbon dioxide, nitrous oxide, and methane, for example) trap energy from the sun. Normal warming is mostly caused by natural gases.
        
             
        
        
        
Answer:
The correct answer would be population density.
Explanation:
 
        
             
        
        
        
They didn't have to worry about farming because they had slaves to do it for them.
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