The students were writing a test at 12 o'clock yesterday, weren't they?
Were the students writing a test at 12 o'clock yesterday?
Who was writing a test at 12 o'clock yesterday?
Were the students or the teachers writing a test at 12 o'clock yesterday?What were the students writing at 12 o'clock yesteday?
What were the students doing at 12 o'clock yesterday?
When were the students writing a test ?
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The students had written a test by 12 o'clock yesterday, hadn't they?
Had the students written a test by 12 or 14 o'clock yesterday?
What had the students done by 12 o'clock yesterday?
Had the students written a test by 12 o'clock yesterday?
Who had written a test by 12 o'clock yesterday?
What had the studens written by 12 o'clock yesterday?