An organ or group of specialized cells in the body that produces and secretes a specific substance, such as a hormone
 
        
             
        
        
        
Convection keeps the earths surface warm
        
                    
             
        
        
        
Answer:
A I believe it is correct
 
        
                    
             
        
        
        
Answer:
There is no short answer.
Explanation:
The primary difference between the periodic and perpetual inventory system is that the perpetual system keeps track of things from the start to finish continuously while the periodic system divides it into periods and keeps the records at the end of every set period of time.
I hope this answer helps.