5. Let the function $y=f(x)=\frac{x^{2}-x+n}{x^{2}+x+1}(x \in R$ and $\left.x \neq \frac{n-1}{2}, n \in N\right)$ have the minimum value $\Omega_{n}$, the maximum value $b_{n}$, and let $c_{n}=\left(1-a_{n}\right)\left(1-b_{n}\right)$. Then the sequence $\left\{c_{n}\right\}$ ).
(A) is an arithmetic sequence with a non-zero common difference
(B) is a geometric sequence with a common ratio not equal to 1
(C) is a constant sequence
(D) is neither an arithmetic sequence nor a geometric sequence