Answer:
muscles -D
Explanation:
the circulatory system consists of three independent systems that work together the heart, the lungs, and arteries, veins , coronary and portal vessels . 
 
        
                    
             
        
        
        
They will continue to exercise throughout life
        
                    
             
        
        
        
<span>Stretching that uses neuromuscular reflexes to gain further stretching of the muscle is called "PNF stretching".
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PNF stands for Proprioceptive Neuromuscular Facilitation and it refers to a further developed type of flexibility training that includes both the extending and contraction of the muscle assemble being focused on. Proprioceptive Neuromuscular Facilitation extending was initially created as a type of recovery, and to that impact it is exceptionally viable. Proprioceptive neuromuscular Facilitation (PNF) is a powerful method for utilizing reflexes to help muscular relaxation.