Physicians Routinely Give Their Patients Pulmonary Function Tests in Order

Physicians routinely give their patients pulmonary function tests in order to measure characteristics of lung function. The most common of these tests, spirometry, measures both the volume and the speed of air entering and exiting the lungs. In this test, a person first breathes normally while breathing into a spirometer, a machine that measures air volume and air speed. Then the person takes the deepest breath possible and exhales as hard as possible for 6 seconds into the spirometer. The resulting data are plotted on a graph of volume (y axis) versus time (x axis) . Spirometry is useful not only for assessing lung function in healthy patients but also for characterizing patients with lung conditions such as pulmonary fibrosis, asthma, or emphysema.
A sample graph for a healthy adult male is shown below. Normal breathing occurs between points A and B, a maximal inhalation occurs at point C, and a maximal exhalation occurs at point D. Normal breathing resumes between points E and F.

-How is spirometry a potentially flawed experimental method to measure lung volume?

A) The test does not sample data for when the patient is breathing normally.
B) There is no way to calculate vital capacity using this method.
C) Patients with lung diseases or disorders cannot take spirometry tests.
D) The patient may be noncompliant and not put forth their best effort in the test.