Explanation:

- Conventional sources of energy refer to traditional sources that have been in use for a long time.

- These can be divided into commercial and non-commercial sources:

- Commercial Source: These include coal, natural gas, and oil. They are traded in the market for a price, widely used for industrial and domestic purposes.

- Non-Commercial Source: These are not sold in the market or have minimal trading, like firewood, agricultural waste, and animal dung, often used in rural settings.

- Both commercial and non-commercial sources are considered conventional.

- Correct Answer: Option 3