Final answer:
A drug that activates only beta-2 receptors could be given to a patient to relieve breathing difficulty due to narrowing of bronchioles.
Step-by-step explanation:
A drug that activates only beta-2 receptors could be given to a patient to relieve breathing difficulty due to narrowing of bronchioles (airways of lungs). Beta-2 adrenergic receptors are responsible for causing smooth muscle relaxation in the bronchi, which helps to widen the airways and make breathing easier.