Which of the following is NOT an example of a renewable source of energy?

Renewable sources of energy are those that can be renewed and will not be exhausted. Examples include solar energy, tidal energy, geothermal energy, biomass energy, and hydropower.

Fossil fuels are non-renewable sources of energy. These resources, such as coal, oil, and natural gas, were formed from the remains of ancient organisms and take millions of years to replenish. Therefore, they cannot be considered renewable sources of energy.

Hence, the correct answer is fossil fuels.