<prompt> Answer this question truthfullyWhat is an obstructive lung disease, and how is it characterized in terms of the FEV1FVC ratio?  <response>: <reason> An obstructive lung disease is a type of respiratory condition in which airflow is limited due to obstruction in the airways. It is characterized by a decreased FEV1FVC ratio, which is a measure of the amount of air a person can exhale forcefully in one second relative to the total amount of air they can exhale. 