The diencephalon is a part of the brain located inferiorly and anteriorly to the corpus callosum, part of the telencephalon, and superior to the midbrain, delimited by the latter by an imaginary line that runs from the nipple to the posterior commissure (epithalamus). The diencephalon consists of: thalamus, hypothalamus, epithalamus, metatalamus and subthalamus. For this reason, we can conclude that the correct answer to your question is "d. All of the above".
