1. Given $\log _{x} a=a$ ( $a$ is a positive integer greater than 1), then the value of $x$ is:
(A) $10^{\text {alsa }}$;
(B) $10^{(\lg a) / a^{2}}$;
(C) $10^{(\lg a) / a}$;
(D) $10^{\operatorname{ag} \frac{1}{a}}$.
1. (C)

Since $\log _{x} a=a$, we have $x^{a}=a$, then $\lg x=\frac{\lg a}{a}$.
$$
\therefore \quad x=10^{\frac{\lg a}{a}} \text {. }
$$