Which is a compound sentence?

 - Rumors about Mayor Wilkinson were spreading like wildfire, so she set the record straight at a press conference.
 - Madison Chock and Gracie Gold were two American figure skaters in the Sochi 2014 Olympics.
The first sentence is the compound sentence. It is made up of two independent clauses joined by the coordinating conjunction so.
Rumors about Mayor Wilkinson were spreading like wildfire, so she set the record straight at a press conference.