What is the proper definition of acid rain? 

A)  the wet deposition of secondary pollutants onto the Earth's surface 
B)  the wet and dry deposition of secondary pollutants onto the Earth's surface 
C)  the dry deposition of secondary pollutants onto the Earth's surface 
D)  the wet and dry deposition of primary pollutants onto the Earth's surface

Acid rain is defined as the wet and dry deposition of secondary pollutants (such as sulfuric acid and nitric acid) onto the Earth's surface. Both wet deposition (rain, snow, fog, and sleet) and dry deposition (particulate matter, gases, and dust) contribute to acid rain. Primary pollutants, on the other hand, are directly emitted into the atmosphere from sources such as factories and cars, and can contribute to the formation of secondary pollutants. However, primary pollutants alone do not define acid rain.