17. (6 points) In the equation below, what digits do $A$, $B$, $C$, $D$, and $E$ each represent?
$A=$ $\qquad$ , $B=$ $\qquad$ , $C=$ $\qquad$ , $D=$ $\qquad$ , $E=$ $\qquad$ .
$$
\begin{array}{r}
A B C D E \\
\times \quad 4 \\
\hline E D C B A
\end{array}
$$
【Solution】Solution: According to the five-digit number multiplied by 4, the product is still a five-digit number, so $A$ can only be 2 or 1. When $A=2$, according to the multiplication table of 4, we get: $E=8$. Then, based on the non-carrying multiplication of $B \times 4$, $B$ can only be 1, because $7 \times 4+3=31$, so $D=7$,

Also, because $C \times 4$ needs to carry 3 to the previous digit, so $c=9$, thus we get:
$$
21978 \times 4=87912 \text {, }
$$

Therefore, $A=2, B=1, C=9, D=7, E=8$.
The answer is: $2 ; 1 ; 9 ; 7 ; 8$.