After You Apply the Pulse Oximeter to a Patient Complaining

After you apply the pulse oximeter to a patient complaining of chest discomfort, she asks you what you are assessing. You would respond by telling her that the pulse oximeter:

A) provides the most accurate evaluation of the heart rate.
B) is a tool used to see if the airway needs to be opened.
C) measures the amount of oxygen circulating in the blood.
D) can tell how much carbon dioxide she is exhaling.