La question commence par WHEN : je réponds avec DURING.
When was he killed ?>>> He was killed during WW1.
When will you apply for that job ?>>> I'll do it during the next holidays, I think.
When should I ask him ?>>> Why not ask him during the interval ?
La question commence par HOW LONG : je réponds avec FOR.
How long will it last ? >>> Well, it'll last for at least two hours.
How long did they stay ?>>> They stayed for less than ten minutes.,
How long had he been watching the street ?>>> I don't know really, I think he'd been watching the street and the bank for quite a long time.