Are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group, and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue. ... They can form lipid bilayers because of their amphiphilic characteristic.
        
             
        
        
        
they are so unique and seen often
 
        
             
        
        
        
Hello there!!!
I'm inclined to think that the answer is A. These are products, so they can't really be reactants (unless the equation is reversible, which this is not). Cellular respiration is the process of the cells releasing the waste that they do not need. So A seems to be the logical choice.
Does this help you?