The correct option is B Fossil fuels
Conventional sources of energy have been around for a very long time. These include fossil fuels like coal, petroleum and natural gas. Energy resources that are considerably new in terms of usage are called Non-conventional Energy resources. For example, solar, wind, tidal, geothermal, biogas and atomic energy. We have started to utilise the potential of these energy sources in recent years. So Ritu would most likely have chosen a fossil fuel to keep her machine running.