阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空，并将答案填写在答题卷标号为16—25的相应位置上。
One of the many things we take for granted in the twentieth century is the speedy collection and delivery of letters to and from all parts of the world at _______ ( astonish ) cheap rates.
A husband away ____ a business trip can write home to his wife two thousand miles away knowing that the letter will reach _____ in a few days. His special airletter may cost him less than a loaf of bread ____ his own bus fare to work.
This service, however, is a favor of comparatively recent origin. Until modern times, the cost of sending letters privately was so great that the _____ ( arrive ) of a letter was a considerable event and might even cost financial hardship to the receiver ______ had to bear the charges.  _____ the Middle Ages on，there were indeed special messengers ______ ( carry ) state correspondence, and other messengers employed to travel with between the great monasteries or the great merchants’ houses, but for centuries there was no official post service by which private letters could be sent. It was not until 1840 ______ the official organization known as the Penny Post ____ ( establish ) in Great Britain and gave ordinary people cheap and efficient postal deliveries.