Select the most appropriate synonym of the given word.

Eagerly

The correct answer is Keenly.

To find the most appropriate synonym, let's analyze the meaning of the given word and the provided options:
1. Eagerly means doing something with a lot of interest, enthusiasm, or impatience (e.g., "waiting eagerly for the results").
2. Keenly means doing something in an eager, intense, or enthusiastic manner (e.g., "keenly interested"). Since both words describe a state of strong interest and enthusiasm, "keenly" is the closest synonym.
3. Stringently means strictly, precisely, or under severe rules/conditions, which is unrelated to eagerness.
4. Dubiously means with hesitation, doubt, or suspicion, which is the opposite of doing something eagerly.
5. Playfully means in a fun, lighthearted, or humorous way, which does not capture the intense interest of eagerness.

Therefore, Keenly is the most suitable synonym for Eagerly.