Answer:
The correct answer is I think D 
Explanation:
Have a great day! :)
 
        
                    
             
        
        
        
a. Competition: Humans compete with all organisms for space.
b. Parasitism: Humans have many parasites: head lice, ticks, tapeworms, etc.
c. Mutualism: We have mutualistic relationships with all domesticated plants/animals.
d. Commensalism: Pigeons thrive in metropolitan ecosystems without really
affecting humans (except for being mildly disgusting).
 
        
             
        
        
        
Answer:
Tributary-river-river system 
i think this is the answer 
Explanation: