the parents were hanging greetings cards on the walls for 5 hours yesterday
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Who were hanging greeting cards on the walls for 5 hours yesterday?
What were the parents hanging on the walls for 5 hours yesterday?
What were the parents doing for 5 hours yesterday? 
How long were the parents hanging greeting cards on the walls yesterday?
When were the parents hanging greeting cards for 5 hours?
Where were the parents hanging the greeting parts for 5 hours yesterday?
Were the parents hanging greeting cards or pictures on the walls for five hours yesterday? 
Were the parents hanging greeting cards on the walls for five or less (more) hours yesterday? 
Were the parents or other people (sister, brother, friends, relatives) hanging greeting cards on the walls for 5 hours yesterday?