Answer:
By exercising, it increases blood flow towards the muscles and digestive tract. This can help move food through the stomach, or digestive tract.  
 
        
             
        
        
        
Answer:
The concentration of a substance is the quantity of solute present in a given quantity of solution. 
 
        
             
        
        
        
I think it’s all of the above because they can all be found in the air and in water sources