When you have a post-office box, the postman doesn't bring letters to you, but you go to the post-office and get your letters and parcels from your box. The box is locked, only you have the key, so the letters and parcels are safe. One day the headmaster of a school wrote to the post-office and asked for a post-office box for his school. He soon got an answer. It said, "We will give you a post-office box in one month." Three months later, the headmaster wrote to the post-office and said, "Why haven't we got a post-office box yet?" This was the answer from the post-office: "Dear sir, We gave you a post-office box two months and wrote to you then to tell you. Here is the key to your box. You will find our letter to you in it." When the post-office said that you could get a post-office, he meant   _  .
you may go to the post-office to get your mails you must wait to get the post-office box you must write again to get the key you must pay for the box before you got it