A. the distance between towns
nasal cavities (or oral cavity) > pharynx > trachea > primary bronchi (right & left) > secondary bronchi > tertiary bronchi > bronchioles > alveoli (site of gas exchange)
coefficient: they balance the chemical equation you have to make sure the number is as small as it can. It is also used to convert different compounds to compounds or quantities to quantities.
They are examples of elements.