Which of the following correctly identifies the most productive layer of a soil profile?

topsoll, just below undecomposed organic matter

subsoll, between topsoil and parent material

undecomposed organic matter, at the very top

parent material, just above bedrock

Just below the O horizon is "topsoil" or "A" horizon.

Usually it is darker than the lower layers, loose and crumbly with varying amounts or organic matter. Plants roots, bacteria, fungi, and small animals are abundant here, and plants thrive in it. It is generally the most productive layer of soil.