Answer:
Calcium is a chemical element with the symbol Ca and atomic number 20.
Explanation:
 
        
                    
             
        
        
        
Dogs, no matter what breed they are, they are all of the same species and therefore can breed with each other and create fertile offspring
 
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The first one is commensalism. The second one is mutualism. The last one is parasitism.
        
             
        
        
        
The surviving R strain transformed into a living S strain.