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c. [4 marks] Explain with the aid of a well-labelled diagram how an increase in the discount rate will affect the optimal rotation period. d. [4 marks] Explain with the aid of a well-labelled diagram how an increase in the cost of harvesting a forest will affect the optimal rotation period. e. [4 marks] Explain with the aid of a well-labelled diagram how an increase in the price of timber will affect the optimal rotation period. f. [4 marks] Explain with the aid of a well-labelled diagram how the presence of positive externalities will affect the optimal rotation period