1.84 The value of the algebraic expression $\frac{4 \sqrt{10}}{\sqrt{13}+\sqrt{8}+\sqrt{5}}$ is
(A) $\sqrt{8}+\sqrt{5}-\sqrt{13}$.
(B) $\sqrt{13}-\sqrt{8}-\sqrt{5}$.
(C) $\frac{1}{2}(\sqrt{8}+\sqrt{5}-\sqrt{13})$.
(D) $\frac{1}{2}(\sqrt{13}-\sqrt{8}-\sqrt{5})$.
(Chinese Zhejiang Ningbo Junior High School Mathematics Competition, 1984)
[Solution]
$$
\begin{aligned}
& \sqrt{8}+\sqrt{5}-\sqrt{13} \\
= & \frac{(\sqrt{8}+\sqrt{5}-\sqrt{13})(\sqrt{8}+\sqrt{5}+\sqrt{13})}{\sqrt{8}+\sqrt{5}+\sqrt{13}} \\
= & \frac{(\sqrt{8}+\sqrt{5})^{2}-(\sqrt{13})^{2}}{\sqrt{8}+\sqrt{5}+\sqrt{13}} \\
= & \frac{4 \sqrt{10}}{\sqrt{13}+\sqrt{8}+\sqrt{5}} .
\end{aligned}
$$

Therefore, the answer is $(A)$