$33 \cdot 18$ If $\sqrt{x^{2}+y^{2}}$ is a positive integer. Then among the following four sets of values, $x$ and $y$ can only be
(A) $x=25530, y=29464$.
(B) $x=37615, y=26855$.
(C) $x=15123, y=32477$.
(D) $x=28326, y=28614$.
(China Beijing Junior High School Mathematics Competition, 1990)