The correct option is D Volcanic eruptions
Forest fires and volcanic eruptions are examples of natural causes of air pollution. Some others are sand storms, salt spray, methane produced by livestock, etc.
Sulphur and nitrogen oxides mix with moisture in the atmosphere to form weak acids which then come down along with rain as "Acid rain". These oxides are released in the form of vehicle and industrial emissions.
Particulate matter are very small size particles that are released from construction sites, smoke stacks, tar manufacturing industries, unpaved roads, etc.