The answer is b, numerous meaning more in amount
        
                    
             
        
        
        
Answer:
Oxygen
Explanation:
A waste product of photosynthesis organisms need for cellular respiration is oxygen. We breathe out carbon dioxide and plants use carbon dioxide during photosynthesis and in return they give us oxygen which is their waste product. 
 
        
             
        
        
        
It has been linked to lung cancer. 
hope this helps!