      
   2        

                          
[1,O]
[2,O]
[3,O]
[4,O]
[5,O]

 

[2,O]
[3,O]
[6,O]
[7,O]

    2      
[1,D]
[4,D]
[5,D]
[6,N]
[7,N]
             2     
 
[1,O]
     2      
[1,D]
     2  
     2             
[6,O]
   
[6,N]



