1. My friends have already gone abroad. 
My friends haven't gone abroad yet. Have my friends already gone abroad? Have my friends already gone abroad or to the neighbouring town? Where have my friends gone? Who has already gone? My friends have already gone abroad, haven't they? My friends haven't already gone abroad, have they?

2. She had done this work by 5 o’clock yesterday.
She hadn't done this work by 5 o’clock yesterday. Had she done this work by 5 o’clock yesterday? Had she done this work by 5  or 6 o’clock yesterday? What had she done by 5 o’clock yesterday? Who had done this work by 5 o’clock yesterday? She had done this work by 5 o’clock yesterday, hadn't she? She hadn't done this work by 5 o’clock yesterday, had she?

3. I will have written the letter by the end of next week. I won't have written the letter by the end of next week. Will I have written the letter by the end of next week? Will I have written the letter by the end of next week or by the end of next month? What will I have written by the end of next week? Who will have written the letter by the end of next week? I will have written the letter by the end of next week, won't I? I won't have written the letter by the end of next week, will I?