C) medium. 
The medium of a wave is any substance that carries the wave, or through which the wave travels.Ocean waves are carried by water, sound waves are carried by air, and. the seismic waves of an earthquake are carried by rock and soil.
        
             
        
        
        
Answer:
A. Encourage an increase in pollution in these countries
 
        
             
        
        
        
Answer: The cells that make up the digestive, muscular, skeletal, reproductive, and excretory systems all need oxygen from the respiratory system to function, and the cells of the respiratory system—as well as all the other systems—need nutrients and must get rid of metabolic wastes.
Explanation:
 
        
             
        
        
        
B). Have a variable volume, meaning they fill up the area they are in.