Which is a compound sentence?

 - The corridor in the basement was dark and damp, so Lauren put on a sweater and found a flashlight.
 - Rosanne and her sisters drew a map of the United States and hung it on the wall.
The first sentence is the compound sentence. It is made up of two independent clauses joined by the coordinating conjunction so.
The corridor in the basement was dark and damp, so Lauren put on a sweater and found a flashlight.