Final answer:
The primary assessment in a medical context involves initially observing the patient as you enter the room, which allows you to gather vital information about their condition before further examination.
Step-by-step explanation:
Concerning the primary assessment, option C is true: The primary assessment begins by just observing the patient as you enter the room. Contrary to A, external bleeding may not always be immediately obvious and requires closer examination. Regarding B, manual airway maneuvers are not performed on all patients, only on those who require it based on the assessment of their breathing. Option D is incorrect because a sternal rub is only used to test for response to painful stimuli on unresponsive patients, not on all patients.