10 Let $f(x)=x^{2}+b x+c$, if the equation $f(x)=x$ has no real roots, then the equation $f(f(x))=x(\quad)$.
(A) has four distinct real roots
(B) has two distinct real roots
(C) has one real root
(D) has no real roots
(10) D Hint: $f(x)=x$ has no real roots, then the graph of the quadratic function $f(x)=x^{2}+b x+$ $c$ is above the line $y=x$, i.e., $f(x)>x$, so $f(f(x))>f(x)>x$.