Question

is this a complete sentence or a fragment?
sang a song about peanut butter and jelly.
complete sentence fragment

Explanation:

A complete sentence needs a subject (who/what does the action) and a predicate (the action). The phrase "Sang a song about peanut butter and jelly" lacks a subject (e.g., "She" or "They" to perform the action "sang"), so it's a fragment.

Answer:

Fragment