Coastal Ocean!
Explanation: It’s important to remember that although the ocean produces at least 50 percent of the oxygen on Earth, roughly the same amount is consumed by marine life. Like animals on land, marine animals use oxygen to breathe, and both plants and animals use oxygen for cellular respiration. Oxygen is also consumed when dead plants and animals decay in the ocean.
This is particularly problematic when algal blooms die and the decomposition process uses oxygen faster than it can be replenished. This can create areas of extremely low oxygen concentrations, or hypoxia. These areas are often called dead zones, because the oxygen levels are too low to support most marine life.
NOAA’s National Centers for Coastal Ocean Science conducts extensive research and forecasting on algal blooms and hypoxia to lessen the harm done to the ocean ecosystem and human environment.
        
             
        
        
        
The answer is Arteries 
Arteries carry oxygen-rich blood from the heart to capillaries. On the contrary, veins carry blood without oxygen from the capillaries to the heart. 
Arteries are very flexible and yet strong blood vessels so that efficient transport of oxygen-rich blood along the bloodstream through the organism is enabled.
        
                    
             
        
        
        
It belongs to 100-999 SCI Code. So its Primary category. Because its all about the farm and geographical industry that focuses on land production, deformation and production in growing the status of our economy and provide the need of people.