20. From 1000 to 9999, the probability of randomly selecting a four-digit number where all digits are different and the unit digit is odd is ( ).
(A) $\frac{14}{75}$
(B) $\frac{56}{225}$
(C) $\frac{107}{400}$
(D) $\frac{7}{25}$
(E) $\frac{9}{25}$
20. B.

From 1000 to 9999, there are 9000 ways to choose a four-digit number. Since the four-digit number to be chosen is odd, the unit digit must be chosen from $1, 3, 5, 7, 9$, which gives 5 ways; the first digit must be chosen from $1,2, \cdots, 9$ excluding the chosen unit digit, which leaves 8 ways; the hundredth and tenth digits have 8 and 7 ways respectively. Therefore, the probability is
$$
p=\frac{5 \times 8 \times 8 \times 7}{9000}=\frac{56}{225} .
$$