The answer is a. They are continuously replenished by natural processes.
Renewable energy resources can be defined as resources that are continuously replenished by natural processes. These resources are sunlight, rain, geothermal heat, wind, tides, and waves. They should be distinguished from non-renewable energy resources which could not be replenished by natural processes, such as natural gas, fossil fuels, coal, etc. They could not be regenerated unlike sunlight or wind for example.
