Which of the following is part of assessing a patient's airway?

Performing a head tilt-chin lift is a standard technique in airway assessment and management. This maneuver is designed to open the airway in patients who are unresponsive or have compromised breathing. By tilting the head back and lifting the chin, the tongue is positioned forward, which helps to clear any obstruction in the airway. This technique is particularly important because maintaining a clear airway is a critical step in the assessment and treatment of respiratory emergencies.

Other options do not directly relate to the initial assessment of a patient's airway. For example, while applying oxygen may be necessary for treatment once an airway is established, it does not assist in the actual assessment of the airway's patency. Checking blood circulation is a separate step in patient evaluation, focusing on perfusion rather than airway. Looking for signs of a stroke involves assessing neurological function, which is important but not directly part of airway management. Therefore, the head tilt-chin lift is the most relevant and essential action when assessing and ensuring a patient's airway is clear and open.