African lungfish, which are often found in small stagnant pools of fresh water, produce urea as a nitrogenous waste. What is the advantage of this adaptation?
\begin{equation}\begin{array}{l}{\text { (A) Urea takes less energy to synthesize than ammonia. }} \\ {\text { (B) Small stagnant pools do not provide enough water to dilute }} \\ {\text { ammonia, which is toxic. }} \\ {\text { (C) Urea forms an insoluble precipitate. }} \\ {\text { (D) Urea makes lungfish tissue hypoosmotic to the pool. }}\end{array}\end{equation}