Respiration in insects is called direct because
a. The cell exchanges O2/ CO2 directly with the air in the tubes
b. The tissues exchange O2/ CO2 directly with coelomic fluid
c. The tissues exchange O2/ CO2 directly with the air outside through body surface
d. Tracheal tubes exchange O2/ CO2 directly with the haemocoel, which then exchange with tissues
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Option (d) is the answer.