The correct answer is A. Compound.
A simple sentence consists of subject/s + verb/s + predicate. It is one complete thought. Ex: We took a chance.
A compound sentence has more than one complete sentence, known as independent clause. They are joined by coordinating conjunction such as but, and, for, or, etc. Ex: We took a chance, and we were sorry.
A complex sentence consists of at least one independent clause and one or more dependent clauses. The dependent clauses are joined to the independent clause by subordinating conjunctions like because, since, if, before, etc. Ex: We took a chance because we needed the results.
In this case, "because we needed it" has no meaning on its own since it is a dependent clause.