28. The number of different integer pairs $(x, y)$ that satisfy $0<\mathrm{x}<\mathrm{y}$ and $\sqrt{1984}=\sqrt{\mathrm{x}}+\sqrt{\mathrm{y}}$ is
(A) 0,
(B) 1;
(C) 3;
(D) 4;
(E) 7.
C
28. From $\sqrt{1984}=8 \sqrt{ } 31$ and $0<x<y$, we can get $\sqrt{1984}=\sqrt{31}+7 \sqrt{31}=2 \sqrt{31}+6 \sqrt{31}$ $=3 \sqrt{31}+5 \sqrt{31}$, thus there are three pairs of positive integers $(\mathrm{x}, \mathrm{y})$, i.e., (C).