The correct answer is A. Sneezing.
Sneezing is a sudden, forceful, involuntary expulsion of air from the nose and mouth caused by irritation of the nasal mucosa. It is a common reflex that helps to clear the nose of irritants such as dust, pollen, and mucus.
Trepidation is a state of fear or anxiety. It is often accompanied by physical symptoms such as trembling, sweating, and a racing heart.
Reversal is the act of turning something back to its original state. It can also refer to the act of changing one’s mind about something.
Hardening is the process of becoming firm or solid. It can also refer to the process of becoming more difficult or resistant.
Sneezing is the only option that is a synonym of sternutation. The other options are not related to sternutation.