"Conventional" sources of energy do not include which of the following options?

1. Electricity
2. Cowdung cake
3. Tidal power
4. Solar power
5. Firewood

C and D only

Both commercial and non-commercial sources of energy are known as conventional sources of energy. Commercial sources are coal, petroleum and electricity as they are bought and sold. Non-commercial sources of energy are fuelwood, agricultural waste, and dried dung. These are non- commercial as they are not available in the market on a large scale. There are three other sources of energy which are commonly termed as non-conventional sources — solar energy, wind energy and tidal power.