It is a sentence because it has a subject and a verb. If it just said Went to the mall, then it would be a fragment.
Fragment you need to make it into a sentence like john and mary both went to the mall together. I hoped i helped you
The phrase "John and Mary went to the mall" is a complete sentence because it contains a subject and a verb, expressing a full thought. In contrast, a fragment lacks such completeness. A sentence fragment would be something like "Went to the mall," which does not convey a complete idea.
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