8. A two-digit number, when the tens digit and the units digit are swapped, the resulting two-digit number is $\frac{7}{4}$ times the original number. How many such two-digit numbers are there?
(A) 1;
(B) 2;
(C) 4;
(D) infinitely many;
(E) 0.
Answer ( $\quad$ )
8. (C)

Let the tens digit of the original number be $a$, and the units digit be $b$, then
$$
\frac{7}{4}(10 a+b)=10 b+a \text {, }
$$

which simplifies to $2 a=b$.
$\because \quad 1 \leqslant a, b \leqslant 9$.
$\therefore a=1,2,3,4$. Then $b=2,4,6,8$.
Therefore, the numbers that meet the condition are $12,24,36,48$, a total of four.