Reticular activating system is the part of the midbrain.
Answer: Option A
Step-by-step explanation:
The Reticular activating system is the system which contains of certain circuits and these circuits develop in the different areas of the brain stem. The areas where these circuits develop also includes the mid-brain meticular formation.
This system basically performs the function of regulating wakefulness and also makes transition of between sleeping and waking. This is all done by the nuclei which are in a proper set and these are connected to each other which are present in the brain of vertebrates.