Read this sentence from “Black Sunday: The Storm That Gave Us the Dust Bowl.”

Once the storm subsided, a simple spring day had become the worst day in recent memory.

Which choice best explains the structure of this complex sentence?
A. An independent clause is followed by a dependent clause.
B. A dependent clause is followed by an independent clause.
C. A dependent clause appears in the middle of an independent clause.
D. A dependent clause appears at the beginning and end of an independent clause.