Answer:
Before.
Explanation:
Subordinating conjunctions are those types of conjunctions that act as the joining words for an independent clause and a dependent clause. From the above provided sentence,
Glinda tells the Wicked Witch, "Be gone before somebody drops a house on you!"
the bolded words "Be gone" is the independent clause while the bold, italicized words "somebody drops a house on you!" is the dependent clause. And in between these two clauses is the word "before' which is a conjunction. This is the subordinating conjunction.
