Answer :
The sentence She thought she saw a stranger, but he turned out to be her neighbor who was back from vacation early. is a compound-complex sentence.
It contains two independent clauses (1. She thought she saw a stranger + but + 2. he turned out to be her neighbor) and one dependent clause (who was back from vacation early).
It contains two independent clauses (1. She thought she saw a stranger + but + 2. he turned out to be her neighbor) and one dependent clause (who was back from vacation early).