Carbon dioxide is a byproduct of respiration while oxygen is a byproduct of photosynthesis.
Remember that a byproduct is a secondary product that is made in the synthesis of another. It is unintended and excreted.
        
             
        
        
        
Basing on the information given, fermentative metabolism is a type of anaerobic metabolism that does not use oxygen to produce ATP or bioenergy.Thus, this where its name derives from.  Thank you for your question. Please don't hesitate to ask in Brainly your queries. 
        
             
        
        
        
A sperm and egg combine to make a zygote. (or fertilized egg) 
So, the answer would be "A".
I hope this helps!
~cupcake
        
             
        
        
        
A have the MC1R gene and melanin deference