Acid rain is primarily caused by the burning of fossil fuels. When fossil fuels such as coal, oil, and natural gas are burned, they release sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere. These gases react with water, oxygen, and other chemicals to form sulfuric acid and nitric acid, which then fall to the ground as acid rain.
Other options like the use of CFCs, habitat fragmentation, and discarding plastic waste do not directly contribute to the formation of acid rain. CFCs are mainly responsible for ozone layer depletion, habitat fragmentation affects ecosystems, and plastic waste contributes to pollution but not specifically to acid rain.