. Respiratory exchange in earthworms occurs through the skin. Because
(a) their skin has holes called spiracles
(b) their skin is dry and rough
(c) their skin is thin and moist
(d) All of the above
Their skin is thin and moist. Earthworm respires through their skin. The gaseous exchange occurs through the skin which is thin, moist, slimy, therefore gases can easily pass through it.