Nadia is digging a hole in her backyard to plant a new tree. As Nadia is digging, she notices that there is only a six-centimeter layer of soil, but then it turns to mostly clay and becomes more difficult to dig. She notices that there are many different types of small insects living in the layer but almost nothing living in the clay layer. She tests the pH of the
soil to ensure that the tree will survive and notes that the pH is 6.7.
If Nadia kept digging deeper in her backyard, which type of soil would she eventually encounter?
bedrock fragments
humus layer
subsoil
topol