Ответ:

Yes/No питання: Will they be having tea in the garden at 6 o'clock tomorrow?

Запитання про час: When will they be having tea in the garden tomorrow?

Запитання про місце: Where will they be having tea at 6 o'clock tomorrow?

Запитання про обставину: Why will they be having tea in the garden at 6 o'clock tomorrow?

Додаткові запитання: Who will be having tea in the garden at 6 o'clock tomorrow? What kind of tea will they be having?