Final answer:
All rock types, including igneous, sedimentary, and metamorphic, can exist immediately below a nonconformity as they are all involved in the formation of such structures.
Step-by-step explanation:
The rock types that might exist immediately below a nonconformity include igneous, sedimentary, and metamorphic rocks. A nonconformity forms when igneous or metamorphic bedrock is eroded, and then horizontal layers of sedimentary rock are deposited directly on top.
This indicates that the bedrock, which is directly below the sedimentary layers, can be either igneous, like cooled and solidified magma, or metamorphic, which are rocks altered by heat and pressure.
Therefore, the correct answer to which rock types might exist immediately below a nonconformity is d) All of the above, as all three rock types can be involved in the formation of a nonconformity.