Which layer of soil is most likely of greatest importance to plant growth?

a. o (organic matter)
b. a (topsoil)
c. b (subsoil)
d. c (parent rock)

The correct answer is topsoil.

Topsoil is upper layer which lies from 2 inches to 8 inches. Topsoil contains greatest concentration of nutrients and organic matter that is required for the growth of plants. This layer of soil is rich in nutrients and minerals. It is the layer where all the biological activities take place. This layer is rich in microorganisms that are also important for the growth of plants. The concentration of nutrients and organic matter present depends on the type of soil such as black soil, loamy soil.