Like other osmoregulatory animals that live in marine environments, sharks maintain tissue concentrations of sodium, potassium, and chloride that are hypoosmotic to the seawater. In contrast to the bony marine fishes, however, sharks do not need to drink seawater. Why? A. High urea and trimethylamine oxide concentrations keep shark tissues slightly hyperosmotic relative to seawater, so water is absorbed passively. B. Sodium, chloride, and potassium do not influence water balance in shark tissues. C. Shark blood is hypotonic to the surrounding tissues, so water always moves passively into the tissue from the blood. D. Sharks excrete large quantities of salt through their gills in exchange for water