If you can choose more than one answer then choose B&C but if not choose B
        
             
        
        
        
Answer:
Historians have identified several key causes, including: rats, trade networks such as the Silk Road, warfare such as the crusades, poor hygiene and a lack of medical understanding.
Explanation:
 
        
             
        
        
        
This means that carbon has 6 protons, and 6 electrons. This also means that the 2nd shell of a carbon atom is only half full with 4 atoms.
        
             
        
        
        
<span>D. Skilled military leader. Hope this helps. :D
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