Ariel is trying to complete the head nod exercise with full commitment and focus. what is this called?

The head nod exercise is also called neck strengthening exercise. This is a common exercise done before and after workouts by implementing 10-20 head nods. The head nod exercise relieved stress, headache and migraines and improve good posture.  

Moreover, this simple neck strengthening exercise stimulates the vestibular system through moving your head up and down, which can help refine head control and release tension in your shoulders and neck.

the correct answer choices are a- b- and d