Which of the following examples shows a plural possessive noun?

The example that demonstrates a plural possessive noun is the one that indicates ownership by multiple individuals or entities. In this case, "officers' salaries" effectively shows that the salaries belong to more than one officer. The apostrophe follows the "s" in "officers," which signifies that it is a plural possessive noun, as it denotes that the salaries are not owned by a single officer but by a group of them.

This is distinct from the other examples, which illustrate singular possessive nouns such as "Alice's car," where ownership is indicated for just Alice, "the girl's hat," which indicates possession by a single girl, and "the boy's toy," showing that the toy belongs to a single boy. These forms do not reflect ownership by multiple subjects, underscoring why "officers' salaries" is the correct choice for a plural possessive noun.