1) Putting drugs in the locked cupboard is very safe
->It is......very safe to put drugs in the locked cupboard........
Cấu trúc chủ ngữ giả với It: "It's + adj (+for O) + to-V..."
2) They will visit their old teacher next week
->They are.....going to visit their old teacher next week.....
Thì tương lai gần "be going to + V-bare" diễn tả hành động sắp diễn ra hoặc đã đc lên kế hoạch từ trc
3) Nam must stay in bed for a few days
->Nam has....to stay in bed for a few days.....
Have/has to + V-bare: phải làm gì