Today we take for granted that the mail will be delivered __1__
daily at our door. But many years ago it might have been
placed in a tree trunk and underneath a rock. In the early __2__
days of the mail no one could be sure about where or when it will arrive. __3__
At the southern tip of Africa there was once a post office
under a rock. At the old days the route from England to __4__
India was around the Cape of Good Hope. The journey was
stormy and danger. It took six long months. Sailors often __5__
wished to send mail home, but they seldom met ships bound
back to England. So at the cape the sailors would go on
ashore. They headed for a certain large stone. On the __6__
stone scratched the words “Look here under for letters.” __7__
They would leave their letters there, knowing that the
next homeward ship would stop and pick it up. __8__
There was another post office like this at the southern
tip of South America. During the golden rush days, boats __9__
sailed around Cape Horn to California. At Cape Horn was
a keg(小桶) 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. __10__
答案及解析：
1.take for granted 改为take it for granted. take it for granted that: 想当然认为…，在该结构中，it为形式宾语，that引导的从句才是真正宾语。如：Don’t take it for granted that you are bond to win. 别想当然地以为你注定会赢。
2.and 改为or,根据句意知，此处应是选择关系，而非并列关系。
3.will改为would。根据句中In the early days和could 知此句主句时态为一般过去时，故其宾语从句中的将来时应为过去将来时，用would。
4.At改为In。at表时间点，如几时几刻：at five o’clock, at 10∶30表一段时间用in, 如：in two years, in a week, in a few days,自然此处the old days 前应用in。
5.danger 改为dangerous. 由于本句是系数结构，故应用形容词；况且从修辞上看既然stormy 有“风暴的”是形容词，后面and 并列的词性也应是形容词。故应将danger 名词改为其形容词dangerous。
6.go on ashore 改为go ashore 或go on shore, ashore 是副词，意为“上岸，在岸上”。此处“上岸”可用go ashore或go on shore来表达。
7.scratched 改为were scratched或they scratched。若用were scratched，则此句为倒装句，主语是words,用过去时和被动语态。若用they scratched，则words是宾语，该句缺主语，根据上下文，加上they即可。
8.it改为them。句中的pick it up 中“it”指的是主句中的letters。根据单复数一致的原则，应用them指代letters。
9.golden改为gold。golden 是形容词，意为“金色的”，“黄金般的”，gold 作名词，意为“黄金”，作形容词，意为“全制的”。故“淘金热”应为“gold rush”。
10.sail 改为sailing。根据boats sail east could pick up 中could为谓动词，到sail 应变为现在分词，作定语，修饰boats。若无字数限制，改成boats which sailed east 这样的定语从句也可以