Must Greta write a letter at 5 o'clock?
Who must write a letter at 5 o'clock?
when must Greta write a letter?
must Boris go to school in the morning?
who must go to school in the morning?
where must Boris go in the morning?
must Mike have dinner at 12 o'clock?
Who must have dinner at 12 o'clock?
what must Mike have at 12 o'clock?