1. If $x=\frac{23+\sqrt{469}}{5}$, then $25 x^{4}-1996 x^{2}+144$ $=(\quad)$.
(A) 0
(B) 1
(C) 469
(D) 1996
,- 1. A.
From the difference in the number of times the letters appear in the condition and conclusion, we know that we should either increase the degree of the condition or decrease the degree of the conclusion (factorize).
Given $5 x-23=\sqrt{469}$,

squaring gives $5 x^{2}-46 x+12=0$.
Rearranging, $46 x=5 x^{2}+12$.
Squaring again gives $25 x^{4}-1996 x^{2}+144=0$.