1. Let $a_{1}, a_{2}, \cdots, a_{n}$ represent the digits from $0$ to $9$, and the $(n+1)$-digit number $\overline{a_{1} a_{2} \cdots a_{n} 2}$, when multiplied by 2, becomes $2 a_{1} a_{2} \cdots a_{n}$. Then the minimum value of $n$ is ( ).
(A) 15
(B) 16
(C) 17
(D) 18
$-1 . C$.
Using vertical multiplication, as shown in Figure 1, work from right to left.
Figure $1^{\circ}$

Therefore, the minimum value of $n$ is 17.