Respiration in insects Is called direct because
A. the cells exchange `O_(2)//CO_(2)` directly with the air in the tubes
B. The tissues exchange ` O_(2)//CO_(2)` directly with coelomic fluid
C. the tissues exchange `O_(2)//C0_(2)` directly with the air outside through body surface
D. tracheal tubes exchange `O_(2)//CO_(2)` directly with the haemocel which then exchange with tissues.
