Concept:Birds, reptiles, and insects conserve water by excreting nitrogenous waste as uric acid.Explanation:These animals convert toxic ammonia into uric acid (C5H4N4O3).Uric acid is nearly insoluble in water.So it is passed out as a semi-solid paste with very little water loss.This adaptation is especially useful for animals that lay eggs on land.Answer:D. uric acid