Which sequence describes the order of structures through which air travels in the bird respiratory system? trachea, lung, anterior air sacs, bronchus, posterior air sacs, trachea trachea, bronchus, anterior air sacs, lung, posterior air sacs, trachea trachea, posterior air sacs, anterior air sacs, bronchus, lung, trachea trachea, bronchus, posterior air sacs, lung, anterior air sacs, trachea?