Which layer of soil is closest to the surface?
a. o (organic matter)
b. a (topsoil)
c. b (subsoil)
d. c (parent rock)

a. o (organic matter)

Explanation:

Soil horizon can be define as different layers of the soil which are parallel to the earth crust. The layers differ from each other on the basis of color, texture,  organic matter content, minerals and others. The O layer or organic matter is closest to the soil surface. This is because of the fact that this layer is exposed to the accumulation of plant litter like leaves, twigs and animal waste like hair, feces and others. In o horizon the decomposition of these materials takes place by the soil microbes which leads to formation of humus which is a source of organic matter.