This is a young woman whom I have treated for depression, she was last seen a year ago.

A) complete sentence
B) fragment
C) run-on
I say it sounds like a run-on

You're right.

To determine whether the given sentence is a complete sentence, fragment, or a run-on, we need to analyze its structure and coherence.

The sentence given, "This is a young woman whom I have treated for depression, she was last seen a year ago," consists of two independent clauses separated by a comma without a coordinating conjunction.

A complete sentence contains a subject, a verb, and expresses a complete thought. In this case, the first independent clause, "This is a young woman whom I have treated for depression," can be considered a complete sentence as it has a subject ("This" and "woman"), a verb ("is" and "have treated"), and expresses a complete thought.

However, the second independent clause, "she was last seen a year ago," also contains a subject ("she") and a verb ("was seen"), but it does not express a complete thought on its own. It seems to be a dependent clause or a fragment.

Therefore, the given sentence is not a run-on but a fragment as it lacks the necessary coherence and completeness for it to be considered a complete sentence. The correct answer is B) fragment.