Troposphere is what I think it is.
        
             
        
        
        
The correct answer is b, antigens
        
                    
             
        
        
        
Kinetic energy is the answer because it is in motion
        
                    
             
        
        
        
There is a valve at the meeting point between each ureter and the bladder prevents the back flow of urine from the urinary bladder to the kidney