Which of the following is an example of a simple sentence?

The sentence "The movie about the comic book superhero had never interested me until last week." is an example of a simple sentence.
A simple sentence is a sentence that has one independent clause. An independent clause is a group of words that can stand on its own as a complete sentence.
In this sentence, the independent clause is "The movie about the comic book superhero had never interested me until last week." The other clauses in the sentence are dependent clauses, which cannot stand on their own as complete sentences.
The other sentences are not simple sentences because they have more than one independent clause.
- "The movie about the comic book superhero fascinated me, but it bored my best friend." has two independent clauses: "The movie about the comic book superhero fascinated me" and "It bored my best friend."
- "The movie about the comic book superhero that I watched last Friday night was very entertaining." has two independent clauses: "The movie about the comic book superhero" and "I watched it last Friday night."
- "The movie about the comic book superhero." is a fragment, which is a group of words that is not a complete sentence.