In what order do these messages appear?

In what order do these messages appear?

private void Awake()
{
    Debug.Log("awake");
}

private IEnumerator Start()
{
    Debug.Log("start");
    yield return null;
    Debug.Log("next frame");
}

1. awake, start, then next frame on a later frame
2. awake and next frame, then start
3. All three messages appear only on the next frame
4. The method never runs because Start cannot return IEnumerator