3.5 Names of volunteers randomly enter three different Olympic venues to participate in reception work. Then the probability that each venue has at least one volunteer is ( ).
(A) $\frac{3}{5}$
(B) $\frac{1}{15}$
(C) $\frac{5}{8}$
(D) $\frac{50}{81}$
3. D.
The number of ways for 5 volunteers to randomly enter three different Olympic venues is $3^{5}=243$. The scenario where each venue has at least one volunteer can be divided into two categories:

The first category, 3 people go to one venue, and the remaining two venues each have 1 person, the number of ways for this category is $\mathrm{C}_{3}^{1} \cdot \mathrm{C}_{5}^{3} \cdot \mathrm{A}_{2}^{2}=60$;

The second category, 1 person goes to one venue, and the remaining two venues each have 2 people, the number of ways for this category is $\mathrm{C}_{3}^{1} \cdot \mathrm{C}_{5}^{1} \cdot \mathrm{C}_{4}^{2}=90$.
Therefore, the probability that each venue has at least one volunteer is
$$
P=\frac{60+90}{243}=\frac{50}{81} .
$$