1.where must we return in time?
when must we return home?
2.who is fond of music?
what is my friend fond of?
3.where did they stay till 5?
till when did they stay at a college?
4.where do we have lunch?
5.who will go on bussines trip next week?
when will my father go on bussines trip?
6.what did I write to my friend yesterday?
when did I write a letter to my friend?