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A scientific theory. Obviously, the hypothesis would need a considerable amount of increased testing to be proven a scientific law. But, even so, it could become a theory. 
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Answer:
O H20 and CH4, but not O2
Explanation:
Compounds consist of multiple elements. O2 is just two oxygen atoms, meaning two atoms from the same element.
 
        
             
        
        
        
if the Earth had 5% more oxygen in the atmosphere Global warming will happen.