Because an Elevated PaCO₂ increases Ventilatory Drive in Normal Subjects

Multiple Choice

Because an elevated PaCO₂ increases ventilatory drive in normal subjects, the clinical presence of hypercapnia indicates which of the following?
1) Inability of the stimulus to get to the muscles
2) Weak or missing central nervous system response to the elevated PCO₂
3) Pulmonary muscle fatigue

A) 1 and 2 only
B) 1 and 3 only
C) 2 and 3 only
D) 1, 2, and 3