5. Let the function $f(n)=k$, where $n \in \mathbf{N}_{+}, k$ is the $n$-th digit after the decimal point of 0.14951728901, for example, $f(3)=9$. Let $f_{n+1}(x)=f\left(f_{n}(x)\right)$, then the value of $f_{2007}(6)$ is $(\quad)$.
(A) 1
(B) 2
(C) 4
(D) 7
5.A.

Notice
$$
\begin{array}{l}
f(6)=7, f_{2}(6)=f(7)=2, f_{3}(6)=f(2)=4, \\
f_{4}(6)=f(4)=5, f_{5}(6)=f(5)=1, \\
f_{6}(6)=f(1)=1, \cdots \cdots f_{2007}(6)=1 .
\end{array}
$$