$2 \cdot 19$ If $m, n$ are the roots of the quadratic equation $x^{2}+1994 x+7=0$, then the value of $\left(m^{2}+1993 m+6\right)\left(n^{2}+1995 n+8\right)$ is
(A) 2000.
(B) 1994.
(C) 1986.
(D) 7.
(Chinese "Zu Chongzhi Cup" Mathematics Invitational Competition, 1994)
[Solution] From the given, we know:
$$
\begin{array}{l}
m^{2}+1993 m+6=m^{2}+1994 m+7-(m+1)=-(m+1), \\
n^{2}+1995 n+8=n^{2}+1994 n+7+(n+1)=n+1,
\end{array}
$$

Thus, the original expression $=-(m+1)(n+1)=-m n-(m+n)-1=1986$. Therefore, the answer is (C)