Which is a compound sentence?
The subway runs beneath the streets of the city. A chimpanzee escaped from the zoo, so the police are searching for it.
A simple sentence is a sentence with only one subject and predicate.
The pitcher threw the ball to first base.
A compound sentence is two simple sentences joined by a comma and a conjunction such as and, but, or, or so.
The pitcher threw the ball, and the batter hit it.
Some simple sentences have a compound subject or a compound predicate, but they are not compound sentences.
Anna and James will watch the fireworks tonight.
This simple sentence has a compound subject, Anna and James.
The singers bowed and walked off the stage.
This simple sentence has a compound predicate, bowed and walked off the stage.
Some simple sentences have introductory phrases, but they are not compound sentences. The introductory phrase is part of the predicate.
In the winter, Farmer Ben wears his heavy coat.
This is a simple sentence. There is one subject, Farmer Ben, and one predicate, wears his heavy coat in the winter.
The first sentence is the compound sentence. It is made up of two simple sentences joined by a comma and the conjunction so.
A chimpanzee escaped from the zoo, so the police are searching for it.