The correct choice is (a) Wood
Explanation: wood is mainly used as a domestic fuel. It has low calorific value of about 10500 kJ/kg. It consists of about 48.5% C; 6% H2; 1.5% of ash; 43.5% O2 and 0.5% N2. Wood fuel is used in different forms such as firewood, charcoal, chips, sheets, pellets and sawdust. The particular form used depends upon factors such as source, quantity, quality and application.