2.132 The number of real roots of the equation
$$
\sqrt{x^{2}+2 x-63}+\sqrt{x+9}-\sqrt{7-x}+x+13=0
$$

is
(A) 0.
(B) 1.
(C) 2.
(D) More than 2.
(China Beijing High School Mathematics Competition, 1993)
［Solution］If the square root is meaningful, then we have
$\left\{\begin{array}{l}x^{2}+2 x-63 \geqslant 0, \\ x+9 \geqslant 0, \\ 7-x \geqslant 0\end{array}\right.$
$\left\{\begin{array}{l}x \leqslant-9 \text { or } x \geqslant 7, \\ x \geqslant-9, \\ x \leqslant 7 .\end{array}\right.$
$\therefore x=7$ or -9. Substituting into the original equation, only $x=-9$ is suitable. Therefore, the answer is $(B)$.