To answer this question, you need to understand the different types of non-commercial biological fuels commonly used in developing countries.
Option A) Animal dung - This option is correct because animal dung, such as cow dung or buffalo dung, is commonly used as a fuel source in many developing countries. It is readily available and can be used for cooking, heating, and lighting.
Option B) Crop residue - This option is incorrect because while crop residue, such as agricultural waste or leftover plant material, can be used as a fuel source, it is not as commonly used as animal dung in developing countries.
Option C) Coal - This option is incorrect because coal is not a biological fuel. It is a fossil fuel formed from the remains of plants that lived millions of years ago.
Option D) Fuelwood - This option is correct because fuelwood, such as firewood or wood chips, is the most common non-commercial biological fuel in a large number of developing countries. It is used for cooking, heating, and other domestic purposes.
The correct answer is Option D) Fuelwood. This option is correct because fuelwood is the most common non-commercial biological fuel used in a large number of developing countries.