Ecologie Havo 4
     1           2       3      4    
  5                 6          
 7          8                  
                         
  9                10           
                         
     11                      
                         
12              13         14        
                         
  15                         
                  16         
                         
17                18             
                         
 19              20            21    
                         
 22                  23    24        
     25                      
                         
26                           
                         
          27                 
28                   29