Which route of entry allows chemicals to enter the body through airways?

Inhalation is the correct answer because it specifically refers to the process of breathing in substances, such as chemicals, through the airways into the lungs. When chemicals are inhaled, they can enter the bloodstream rapidly due to the large surface area of the lungs and the thin membranes that facilitate gas exchange. This route of entry is significant in occupational health, as it can lead to direct exposure to harmful chemicals present in the air.

In contrast, ingestion involves taking in substances through the mouth, which primarily enters the digestive system rather than the respiratory system. Absorption pertains to the uptake of chemicals via the skin or mucous membranes, while injection refers to substances being directly introduced into the body, often using a syringe. Each of these routes of entry affects the body in different ways, but inhalation directly targets the respiratory system, making it the appropriate choice for this question.