According to Alexander (1991), a tag question is
I. a short question that follows a statement. II. affirmative-negative (Mary was sad, wasn’t she?) or negative-affirmative (Mary wasn’t sad, was she?). III. uttered with a rising intonation when the speaker wants the listener to agree with him, without expecting an answer; however, when it is uttered with a falling intonation, the speaker is asking a real question, and needs an answer.
Which ones are correct?