After 5 Minutes of Hyperventilation Breathing Cold Air,a Subject's FEV₁

After 5 minutes of hyperventilation breathing cold air,a subject's FEV₁ falls 16% from the pre-test value.The pulmonary function technologist should conclude that:

A) The subject has hyperreactive airways.
B) The air was not cold enough to provoke a response.
C) An additional 5 minutes of hyperventilation is required.
D) Inadequate CO₂ was added to the inspired gas.