Final answer:
The correct punctuated sentence is 'After the horse was stolen, we locked the barn door.'
Step-by-step explanation:
The sentence that is punctuated correctly is sentence C: "After the horse was stolen, we locked the barn door." This sentence uses the correct punctuation by placing a comma before and after the introductory phrase "After the horse was stolen." It also uses proper capitalization and ends with a period.
Learn more about Punctuation in English sentences