4. Let $a, b, c$ be real numbers, $x=a^{2}-2 b+\frac{\pi}{3}, y=b^{2}-$ $2 c+\frac{\pi}{6}, z=c^{2}-2 a+\frac{\pi}{2}$. Then among $x, y, z$, at least -- values ( ).
(A) are greater than 0
(B) are equal to 0
(C) are not greater than 0
(D) are less than 0
4. (A).

Since $x+y+z=(a-1)^{2}+(b-1)^{2}+(c-1)^{2}+\pi$ $-3>0$, then at least one of $x, y, z$ is greater than 0.