$6 \cdot 37 \quad(\sqrt{3}+\sqrt{2})^{2 \log _{(\sqrt{3}-\sqrt{2})}^{\sqrt{5}}}$ is
(A) an irrational number.
(B) a positive integer.
(C) a positive fraction.
(D) a negative fraction.
(China Fujian Province Junior High School Mathematics Competition, 1984)
[Solution] $\because(\sqrt{3}+\sqrt{2})(\sqrt{3}-\sqrt{2})=1$, then the original expression $=(\sqrt{3}-\sqrt{2})^{-2 \log _{(\sqrt{3}-\sqrt{2})} \sqrt{5}}=(\sqrt{5})^{-2}=\frac{1}{5}$. Therefore, the correct choice is $(C)$.