Which of the following sentences is grammatically correct?

Question

Quizplus · Accepted Answer

Run-on sentences are when two or more complete sentences are written as one sentence. Run-on sentences can be fixed by adding a dash (-), a semicolon (;), or a colon (:) between the two sentences. You could also add a coordinating conjunction with a comma (, but) or make them two separate sentences with a period (.)
He studied hard but she studied harder would have been correct if it were written he studied hard, but she studied harder.

Which of the Following Sentences Is Grammatically Correct