Answer:
respiratory system
Explanation:
The function of the respiratory system is to move two gases: oxygen and carbon dioxide.
 
        
             
        
        
        
Replication occurs in three major steps: the opening of the double helix and separation of the DNA strands, the priming of the template strand, and the assembly of the new DNA segment.
 
        
             
        
        
        
It would be the first option. Adenine and thymine.