Answer:
b., c., e. are the answers.
Purines have double rings, whereas pyrimidines have single rings.
 
        
             
        
        
        
Answer:
I think its lipid 
Explanation: I am taking the test right now for grad-point  so tell me if i am wrong .
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The cell membrane protects the cell and keeps bad things like viruses from getting in the cell.<span>It consists of the lipid bilayer with embedded proteins.</span>
        
             
        
        
        
Answer:
hydrogen
Explanation:
the more hydrogen ions then lower the ph and the fewer hydrogen lions the higher the ph.