The average calorific value of wood is about : __________?
A. 33500 kj/kg
B. 25000 kj/kg
C. 23000 kj/kg
D. 19700 kj/kg
A. 33500 kj/kg
B. 25000 kj/kg
C. 23000 kj/kg
D. 19700 kj/kg