Which condition is primarily associated with the respiratory system?

Decongestants are primarily associated with the respiratory system because they are medications specifically designed to relieve nasal congestion and improve airflow in the respiratory passages. They work by narrowing the blood vessels in the nasal passages, leading to reduced swelling and congestion. Decongestants are commonly used to treat conditions such as colds, allergies, and sinusitis, which directly affect the functioning of the respiratory system.

In contrast, the other options relate to different bodily systems or conditions. Dyslexia is a learning disorder that primarily affects reading and language processing; caries refer to dental decay, which affects oral health; and eczema is a skin condition that causes inflammation and irritation. Thus, decongestants stand out as the only choice that directly addresses a problem within the respiratory system.