An exposition is a literary device used to introduce background information about a character, an event or a setting.
Option A: The given lines give background information about a story revolving three bears. Hence it's an exposition and option A is correct.
Option B: A euphemism is a polite expression that replaces a more harsh or offensive one.
Option C: A metaphor is a figure of speech that refers to similarities between unrelated things.
Option D: An anecdote is a short or interesting story about an incident or person.
Options B, C and D do not reflect in the given lines. Hence options B, C and D are wrong.