6. Given an integer-coefficient polynomial, a student obtained the results $f(-2)=-56, f(1)=-2, f(3)=53, f(6)=528$. Then the one he calculated incorrectly is
(A). $f(-2)$.
(B) $f(1)$.
(C) $f(3)$.
(D) $f(6)$.
6. (C).

Let the polynomial with integer coefficients be $p(x)=a_{n} x^{n}+a_{n-1} x^{n-1}$ $+\cdots+a_{1} x+a_{0}$. Clearly, $m-t \mid p(m)-p(t)$. Here, $m$ and $t$ are integers. Using this conclusion to verify each case, it is found that $f(3)=53$ is incorrect.