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This is because of greenhouse gases and polution.
        
                    
             
        
        
        
Answer:
gene pool? species? 
Explanation:
Question is a bit vague hope this helped tho :(
 
        
             
        
        
        
Hi the answer to your question is called the jugular notch and the cricoid cartilage that the thyroid gland is between.
Hope this helps.