The graph of the quadratic function $y=-x^{2}+20 x-64$ passes through the positive integer points (i.e., points where both the x and y coordinates are positive integers) of
(A) an infinite number
(B) 6
(C) 11
(D) 13
4. (C).
$y=-(x-10)^{2}+36$, from $x>0, y>0$ we get $(x-10)^{2}<36$, i.e., $|x-10|<6$, then $4<x<16$, which means $x$ can take 11 positive integers, thus there are 11 positive integer points in total.