Which is a complex sentence?
A: I can review the draft of your story unless you're still editing it.
B: Her dog happily fetched his tennis ball from the muddy puddle and eagerly waited for her to throw it again.
The first sentence is the complex sentence. It is made up of an independent clause and a dependent clause. The dependent clause begins with the subordinating conjunction unless.
I can review the draft of your story unless you're still editing it.