The boys are very upset
1) Are the boys very upset?
2) The boys aren't very upset
3) Who is very upset?
This happens every day
1) Does this happen every day?
2) This doesn't happen every day
3) How often does it happen?
Mary has studied English since her childhood
1) Has Mary studied English since her childhood?
2) Mary hasn't studied English since her childhood
3) What has Mary studied since her childhood?
Tom bought the new car last spring
1) Did Tom buy the new car last spring?
2) Tom didn't buy the new car last spring
3) When did Tom buy the new car?
