The correct answer is A. Wind power which converts wind to electrical energy. Wind is used to turn turbines to produce a generator which generates electricity. No pollution is produced in this way.
The other options, B,C and D produces pollutants when burned or used, the main one being carbon dioxide. Natural gas, fossil fuels and biomass energy are derived from organic materials and as such release carbon dioxide, the main green house gas that contributes to present day global warming.
