The b horizon is a. rockier than the c horizon c. less nutrient rich than the a horizon b. richer in humus than the a horizon d. thicker than the c horizon

The soil is made up of layers, called horizons, which are parallel to soil crust. These horizons are from top to bottom:

O - contains organic matter.

A - contains organic matter mixed with mineral matter.

B - contains accumulated mineral or organic compounds.

C - consists of parental material.

R - consists of bedrock, masses of hard rock.

Thus, through the process of elimination:

a. b horizon is not rockier that the c horizon because c horizon consists of parental material.

b. a horizon is richer in humus because it consists of more organic and mineral material than b horizon.

d. c horizon is thicker than b horizon.

This leaves choice c. less nutrient rich than the a horizon. A horizon is richer in organic and mineral material than b horizon.

layer 3 is younger than layer 6.