Why do membrane bounded organelles facilitate faster chemical reactions

The choices can be found elsewhere and as follows:

a.membranes lower the activation energy of biochemical reactions. 
b.reactants are within close proximity to each other. 
c.membrane-bounded organelles act as catalysts for biochemical reactions. 
d.reactants move faster within membrane-bounded organelles. 
e.reactants are less likely to encounter each other within membrane-bounded organelles. 

The correct answer is option C. Membrane bounded organelles facilitate faster chemical reactions because it act as catalysts for biochemical reactions. Hope this answers the question.

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