Final answer:
pneumatic, referring to the bird's lightweight bones filled with air and connected to their respiratory system, contributing to their flight capabilities.
Step-by-step explanation:
what type of bones birds have due to air passing through small openings is A. pneumatic.
Birds possess a specialized respiratory system that supports their high metabolic rate required for flight. This system includes several air sacs which not only make the bird lighter but also contribute to a highly efficient means of gas exchange. The bird's pneumatic bones are hollow and sometimes connected to these air sacs in the body cavity. Unlike mammals, birds maintain unidirectional airflow through their lungs, which facilitates a counter-current gas exchange with the blood. This creates an effective oxygen-delivery system to sustain their active lifestyle. Additionally, features like the lightweight keratin beak without teeth and the air-filled spaces within their skeleton connecting to their respiratory system contribute to the reduction in body weight, which is vital for flight.
The bones in birds that have small openings for air passage are called pneumatic bones. The air spaces in these bones are connected to air sacs in the body cavity, which helps in efficient respiration and makes the birds lighter. Unlike mammalian lungs, which have bidirectional airflow, birds have unidirectional airflow through their lungs, allowing for more efficient gas exchange.