1. The right answer is the mucus filters the air.
Mucus are different viscous and translucent secretions, little or not very soluble in water, produced by specific glands of various organisms, and in these by various internal organs (eg by the goblet cells of the stomach) or internal mucosa or skin (eg fish, some amphibians, slugs, snails ...).
In humans, mucus produced in the lungs helps to protect the respiratory system by capturing and exporting many of the foreign particles that enter the nose or mouth with each inhalation. In response to inhalation of particles or allergens, mucus secretion increases (reflex and neurohumoral control process), excessively sometimes (in allergic or asthmatic patients).
2. The right answer is less air reaches the lungs (or it blocks the passage of air to the lungs).
Bronchiolitis is an acute infection of the lower airways of viral origin, affecting the small bronchi of infants and young children and spreading in a seasonal epidemic mode.
The clinical picture is due to an obstruction of the airways, on the one hand caused by a mucous plug obstructing the light, on the other hand due to inflammation of the wall. The mucous plug is created by the accumulation of dead cells and mucous secretions. The obstruction is only slightly related to the bronchial spasm, the smooth muscles being little developed at this age.