1. If $m^{2}=n+2, n^{2}=m+2(m \neq n)$, then the value of $m^{3}-2 m n+n^{3}$ is ( ).
(A) 1
(B) 0
(C) -1
(D) -2
-.1.D.
Since $m^{2}-n^{2}=n-m \neq 0$, therefore,
$$
\begin{array}{l}
m+n=-1 . \\
\text { Also } m^{3}=m^{2} \cdot m=(n+2) m=m n+2 m, \\
n^{3}=n^{2} \cdot n=(m+2) n=m n+2 n .
\end{array}
$$

Then $m^{3}-2 m n+n^{3}=2(m+n)=-2$.