Today we take for granted that the mail will he delivered daily at our S1.______ door. But many years ago it might have been placed in a tree trunk and S2.______ underneath a rock. In the early days of the mail no one could be sure about where or when it will arrive. S3.______ At the southern tip of Africa there was once a post office under a rock. At the old days the route from England to India was around the Cape of S4.______ Good Hope. The journey was stormy and danger. It took six long months. S5.______ Sailors often wished to send mail home, but they seldom met ships bound hack to England. So at the cape the sailors would go on ashore. They headed S6.______ for a certain large stone. On the stone scratched the words 'Look hereunder S7.______ for letters.' They would leave their letters there, knowing that the next homeward ship would stop and pick it up. S8.______ There was another post office like this at the southern tip of South America. During the golden rush days, boats sailed around Gape Horn to S9.______ California. At Cape Horn was a keg(烛桶) nailed to a post. Boats coming from the east coast would send some sailors to this post office. They picked up any letters in the keg. At the same time they mailed letters home that boats sail east could pick up. S10.______ 【S1】