1. The quadratic function that satisfies the condition $f\left(x^{2}\right)=[f(x)]^{2}$ is ( ).
(A) $f(x)=x^{2}$
(B) $f(x)=a x^{2}+5$
(C) $f(x)=x^{2}+x$
(D) $f(x)=-x^{2}+2004$
-1.A.
Let $f(x)=a x^{2}+b x+c$. Substitute, expand and determine $a=1$, $b=0$, $c=0$.