Work Step by Step
Option A is incorrect. Urea is excreted in mammals and some amphibians. Option B is incorrect. Animals cannot excrete pure ammonia because it is so toxic that it cannot be stored in any amount in the body. Ammonia must be converted to another type of nitrogen-containing waste product to be able to be stored for any length of time within the body before excretion. Option D. is incorrect. Toxins are poisons and are not excreted. Option C is correct. Reptiles, birds, and insects excrete wastes in the form of uric acid.