A、Two centuries. B、300 years ago. C、In 1691. D、In the 16th century. B文中两处提供了本题的答案，在文章的开始和结尾，我们可以听到以上所列关键词，故B正确。

The first postal service in North America began in New England in the 17th century. All mail arriving in Massachusetts  colony was sent to the home of appointed official in Boston. In turn, he would deliver the mail from Boston on horseback to its destination, receiving one penny for each good article of mail. Later in the century postal services were established between Philadelphia and Delaware.  In 1691, the British crown appointed the first postmaster general  to have charge of the mail for all the colonies in North America.  Later, Benjamin Franklin served as the postmaster general for the British government and then was made postmaster by the newly formed United States government. Franklin was responsible for establishing the United States’ postal systems on a permanent basis. He increased the number of post office, introduced the use of stagecoaches to carry  mail, and started a package service system. They were used to carry mail into the towns. Some communities, especially those out west, were far from the services of transportation.  To serve them, the post office developed a system called "star routes". Private contractors paid to deliver mail to the communities from railways by horse and wagon. The postal service, which was started over 3 centuries ago has developed in to an extensive government service with post of fices in every city town and village in the United States