What is the net primary productivity of the tropical rainforest if gross primary productivity in a tropical rainforest is 6 kcal/m2/yr and respiration is 3 kcal/m2/yr? A) 1.5 kcal/m2/yr B) 2 kcal/m2/yr C) 3 kcal/m2/yr D) 4 kcal/m2/yr