10.I'm so busy , so I don't write to my friends regularly

->If I....weren't so busy, I would write to my friends regularly................................

11.The office may be closed, so Mark won't be able to get in

->If the office.....isn't closed, Mark will be able to get in(Tham khảo c11)......................

12.You can't look the word up because you haven't got a dictionary

->If.........you had got a dictionary, you could look the world up................

-Câu điều kiện loại 1 diễn tả điều có thể xảy ra ở hiện tại hoặc tương lai

-Cấu trúc: If+S+V(hiện tại đơn), S+will/can/may+V(infinitive)