A. The bird flew north of the beach. B. The boys surrendered, but they should of fought. C. The three girls might of broken the records. D. We should of left early.
These were the provided answers.
The correct answer would be "The bird flew north of the beach."
...all of the others if you read them out loud and semi-quickly, you would hear that the sentence sounds like "slang" which therefore makes then incorrect. The correct usage lies within ...flew north of the beach.