Exchange of respiratory gases takes place in an earthworm through (A) moist skin (B) gills (C) trachea (D) lungs

The lungs is the answer

Explanation

Earthworms do not have specialized respiratory organs like we do; instead, they take in oxygen and expel carbon dioxide directly through their skin. Oxygen diffuses through the earthworm's body surface and diffuses inward to the network of capillaries lying just under the body surface.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."