I believe it's the last two. "makes the lungs able to fill more completely" and "helps the blood vessels dilate more easily" hope this helps, have an amazing day :)
The brain stem which is composed of the Pons, The Medulla, and the Midbrain serve a very vital function... They control the functions that keep you alive; Heart Rate, Respiratory Rate, Breathing input and output, Blood pressure, as well a vasomotor functions. So taking this into account, an injury to the brain stem is extremely bad, as that can and will most definitely be very lethal.
Develop a hypothesis, make observations, analyze data, draw conclusions
