SAT English Practice Question

The first sentence in this paragraph is a complex sentence, meaning that it contains a dependent clause and an independent clause. The independent clause is the part that could stand on its own as a complete sentence. The dependent clause is the part that cannot stand on its own as a complete sentence. In this case, the dependent clause is "when the weather turns cold." What is the most likely reason for the use of a comma in the first sentence?

1. A.separate the subject of the independent clause from the verb of the independent clause.
2. B.separate the dependent clause from the independent clause.
3. C.separate the subject of the dependent clause from the verb of the dependent clause.
4. D.separate the verb of the independent clause from the direct object of the independent clause.