The right lung contains three lobes: upper, middle, and lower. The left lungs contains two lobes: upper and lower. The left lung is designed to be smaller than the right in order to accommodate the heart, which is situated slightly to the left.

The respiratory system allows air to enter the lungs from the outside environment and facilitates gas exchange with the blood. Air initially enters through the mouth or nose, passes through the pharynx and larynx, and enters the trachea. From the trachea, air travels through branching structures from bronchi, to bronchiole, to alveoli. Gas exchange occurs between the air in the alveoli and the capillaries surrounding the alveoli.

The pharynx, located posteriorly (behind) the nasal passages and the mouth, is responsible for collecting the air that is taken in via the nose and mouth. The pharynx then passes the air to the larynx before it flows into the trachea. The trachea carries the air to the bronchioles, which end in terminal alveoli in the lungs.

Air enters the body through the nose or mouth, and is transferred to the pharynx (the upper portion of the throat located at the back of the mouth). The larynx is commonly called the "voice box," and is the lower portion of the throat connected to the pharynx. From there, air enters the trachea and flows into the chest. The trachea branches into two bronchi, which continue to branch and divide as the air is carried into the lungs.

The nasal passage's main function is to heat or cool air before it enters the lungs. The cilia, mucous and hair also help filter air since the respiratory system is very sensitive to allergens and infection. Also, the lungs need to be kept moist and lubricated, so dry air is damaging. No gas exchange occurs in the nasal passage, it is merely a conduction zone through which air must travel before it gets to the alveoli where gas exchange occurs with the pulmonary capillaries.

After entering the nose and mouth, air is passed into the pharynx. It then travels to the larynx, which houses the vocal cords, before entering the trachea. The trachea transports the air into the thoracic cavity before branching into the primary bronchi. The right bronchus carries air to the right lung; the left bronchus carries air to the left lung. Of the given answer options, air only passes through the pharynx before entering the lungs.

Alveoli are found in the lungs and the primary site of gas exchange; however, the question specifies a structure before the air enters the lungs. The esophagus transports food, and is not involved in respiration. Nephrons are the function units of the excretory system, and are located in the kidneys.

Anterior to the esophagus, the trachea begins at the larynx (voice box) and extends down towards the lungs where it splits into the bronchi. The trachea is a conducting structure, meaning no gas exchange occurs in the trachea. Instead, it is held open by "C" shaped rings of cartilage to allow maximum airflow between the lungs and the air in the environment. 

The nose is the primary passageway of air into the lungs. Before air can safely enter the body, it must be brought to body temperature, moisturized and cleansed of any particles that could damage the respiratory system or cause infection. Mucous is produced by goblet cells. Olfaction is carried out by specialized neurons in the nose that bind to certain molecules and send information to the brain.

The right lung has 3 lobes and left lung has only 2 lobes to allow room for the heart. The majority of the heart is on the left side of the body since the left ventricle is the largest and thickest-walled chamber of the heart.