secondary energy sources

例句：

1. 1. The city relies heavily on coalas its primary energy source.
   这个城市主要依赖煤炭作为其主要的能源来源。
2. 2. The governmentis exploring alternative sources of energy to reducedependence on fossil fuels.
   政府正在探索替代能源的来源，以减少对化石燃料的依赖。
3. 3. The development of renewable energysources has become a hot topic in recentyears.
   可再生能源的发展近年来已成为热门话题。