Bob and Mary are drinking tea.
Разделительный вопрос: Bob and Mary are drinking tea, aren't they? -Yes, they are. / No, they are not.
Специальный: What are they drinking? - They are drinking tea.
К подлежащему: Who is drinking tea? - They are.
Альтернативный: Are they drinking tea or coffee? - They are drinking tea.
Tom is a worker.
Разделительный вопрос: Tom is a worker, isn't he? -Yes, he is. / No, he is not.
Специальный: What is Tom? - He is a worker.
К подлежащему: Who is a worker? - Tom is.
Альтернативный: Is Tom a worker or a dentist? - He is a worker.