$32 \cdot 39$ The symbol $R_{k}$ represents an integer, whose decimal representation is a string of $k$ 1's, for example, $R_{3}=111, \quad R_{5}=11111$, etc. When $R_{4}$ divides $R_{24}$, the quotient $Q=\frac{R_{24}}{R_{4}}$ is an integer, whose decimal representation contains only the digits 1 and 0. The number of zeros in $Q$ is 
(A) 10.
(B) 11.
(C) 12.
(D) 13.
(E) 15.
(44th American High School Mathematics Examination, 1993)
[Solution]
$$
\begin{aligned}
& \frac{R_{24}}{R_{4}}=\frac{9 R_{24}}{9 R_{4}}=\frac{10^{24}-1}{10^{4}-1}=\frac{\left(10^{4}\right)^{6}-1}{10^{4}-1} \\
= & 10^{20}+10^{16}+10^{12}+10^{8}+10^{4}+1 \\
= & 100010001000100010001 .
\end{aligned}
$$

Therefore, the answer is $(E)$.