Passage One
Questions 57 to 61 are based on the following passage.

There were inns throughout the ancient civilized world, strategically placed to accommodate merchants, military personnel, government officials and others whose work forced them to travel. Traveling for pleasure was almost unheard of. During the early Middle Ages, travel was infrequent and unsafe. About the 12th century traveling again became relatively safe, and inns were established along the main mutes to accommodate merchants, religious pilgrims (朝圣者) and others. Inn standards rose steadily as local economies improved. By the end of the Middle Ages, there were inns throughout Europe and in the Islamic countries, meant primarily for the use of merchants. The Industrial Revolution stimulated inn building, especially in England, whose inns became a standard for the rest of the world. The first hotels in North America Were Atlantic seaport inns and converted farmhouses along stagecoach (马车) routes. When cs and railroads were built along the rights-of-way. As cities grew, new hotels were constructed in the business centers and theater districts. By 1,800 the United States already had the largest hotels in the world, and this trend toward large size continued into the 20th century. The Stevens Hotel (now the Chicago Hilton and Towers) in Chicago once boasted of being the largest in the world, with 3,000 rooms. It has since been exceeded in size by the Hotel Russia in Moscow, and hotels with several hundred rooms have become common nearly everywhere. As travel for pleasure gained popularity in Europe, luxury and resort hotels were built in many countries. The Savoy Hotel in London set new standards of luxury when it opened in 1889 by having its own electricity, theater, private chapel (小教堂) , laundry, and printed press. The hotel was managed by Cesar Ritz, who opened his own luxury hotel in Paris in 1898. The standards set by the Savoy and the Ritz have been imitated by hotels around the world.

Which of the following can mainly account for the unsafe traveling in the early Middle Ages