Concept:Acid rain is caused by acidic gases mixing with water vapour in the atmosphere.Explanation:Oxides of sulphur, such as SO2 and SO3, are released from burning fossil fuels.These oxides dissolve in rainwater to form sulphuric acid, which falls as acid rain.Lead oxide, particulate matter, and gaseous hydrocarbons do not directly produce acid rain.Answer:C. Oxides of sulphur.