How Do Primary Pollutants Differ from Secondary Pollutants

How do primary pollutants differ from secondary pollutants?

A) Primary pollutants include natural sources of air pollution such as volcanoes, whereas secondary pollutants result from human activity.
B) Primary pollutants emit directly from a source, whereas secondary pollutants result from reactions occurring in the atmosphere.
C) Primary pollutants are larger than 50 micrometers in size, whereas secondary pollutants are smaller than 50 micrometers.
D) Primary pollutants are produced by one source, such as a power plant, whereas secondary pollutants are produced by many smaller sources, such as automobile emissions.