The best graph which describes the scenario is diagram C.
Using the parameter given to make our inference;
Number of trees harvested = 14
For A.
Number of trees harvested = 2 + 2 = 4
For B .
Number of trees harvested = 5 + 5 = 10
For C :
Number of trees harvested = 7 + 7 = 14
Therefore, the diagram which shows the correct model is option C.