Answer:
BEFORE
Step-by-step explanation:
A subordinating conjunction is a type of conjunction that joins an independent clause (one expressing a complete thought) to a dependent clause (one not expressing a complete thought), while introducing the latter. Before, after, while, because, since, if, although and until are all examples of this conjunction.
In the sentence, the subordinating conjunction “before” serves to join the independent clause “I had not finished the dishes” to the dependent clause “before the visitors arrived” and to introduce the latter.