Adult insects exchange respiratory gases primarily by means of ____.

A) spiracles only
B) tracheal tubes and spiracles
C) lungs
D) gills
E) body surface

Adult insects exchange respiratory gases primarily by means of tracheal tubes and spiracles. Spiracles are openings along the abdomen and thorax that allow air to enter and exit the respiratory system, while the tracheal tubes distribute oxygen directly to the cells throughout the insect's body. Insects do not have lungs or gills, and although gas exchange can occur across the body surface, it is not the primary method used by adult insects.