Welcome to english-test.net and thanks for posting your questions. The key word here is ‘broke’ which is the simple past of ‘break’ This means we are talking about two actions that happened as a sequence: First they ran for 3 hours and then the storm broke so you need “had been running” to describe the first action.
Let me know what you think.
Thanks,
Torsten[YSaerTTEW443543]
Hi, Torsten
Thank you for quick answer.
But if they keep on running?
They were running for 3 hours when the storm broke.
Is it correct ?
Thank you.
Lika
I think the crucial point is that the length of time is mentioned. If it was omitted, then you could say: They were running when the storm broke. But the indication is that the storm broke after they had been running for 3 hours.