The substance that reduces surface tension in the alveoli is:

A. Apnea refers to a complete cessation of breathing, not just a decrease in depth and rate.
B. Hypoxemia is a condition characterized by low oxygen levels in the blood, but it does not specifically refer to breathing rate or depth.
C. Hypoxia is a broader term indicating low oxygen supply to tissues, which can result from various causes, including but not limited to respiratory issues.
D. Hypopnea specifically means shallow or slow breathing, indicating a reduction in both the rate and depth of respiration. It is often seen in sleep-related breathing disorders and can lead to decreased oxygenation.

A. Allergic rhinitis is an allergic reaction to airborne particles like pollen or dust, and while it affects the upper respiratory system, it is not an infection.
B. COPD (Chronic Obstructive Pulmonary Disease) is a chronic condition that affects the lower respiratory system, especially the lungs, but it is not an infection.
C. Tuberculosis (TB) is a bacterial infection that primarily affects the lungs and is considered a lower respiratory infection, not an upper respiratory infection.
D. Acute Coryza is commonly known as the common cold, which is an upper respiratory infection caused by viruses such as rhinoviruses. It affects the nasal passages, throat, and sinuses.