How can chemical agents enter the human body?

Chemical agents can enter the human body through multiple pathways, making the option highlighting ingestion, inhalation, or absorption the most comprehensive and accurate.

Inhalation occurs when a person breathes in harmful airborne agents, which can lead to immediate effects on the respiratory system. Ingestion refers to swallowing harmful substances, which can affect the digestive system and subsequently have systemic effects on the body. Absorption is when chemicals come into contact with the skin and are absorbed into the bloodstream; this can happen even with substances that might not necessarily cause harm through other routes.

Recognizing all three entry points is crucial for understanding the potential risks posed by chemical agents, particularly in emergency response scenarios. Thus, the option correctly captures the various ways in which harmful substances can impact individuals, ensuring awareness and proper prevention or treatment measures.