Transportation and communication networks bring people together. Yet sometimes people themselves create barriers(障碍) to transportation and communication. In some countries, laws stop people from moving freely from place to place. Over the centuries, many groups of people have been denied the freedom to travel because of their race, religion, or nationality. In the Middle Ages, for example, Jews were often forbidden to move about freely within certain cities. South Africa's government used to require black Africans to carry passes when they travel within the country. Some governments require all citizens to carry identification papers and to report to government officials whenever they move.
Countries set up customs posts at their borders. Foreign travellers must go through a customs inspection before they are allowed to travel in the country. Usually travellers have to carry special papers such as passports and visas(签证). Some countries even limit the number of visitors to their country each year.  Others allow tourists to visit only certain areas of the country, or they may require that travellers be with an official guide at all times during their stay.
Many of those barriers to travel also act as barriers to communication.
When two governments disagree with each other on important matters, they usually do not want their citizens to exchange news or ideas freely. Countries often try to keep military or industrial information secret.
Today, people have the ability to travel, to communicate, and to transport goods more quickly and easily than ever before. Natural barriers that were difficult or dangerous to cross a hundred years ago can now be crossed easily. The barriers that people themselves make are not so easy to overcome. But in spite of all the different kinds of barriers, people continue to enjoy travel and the exchange of goods and ideas.
6. The examples in paragraph 2 are used to tell the readers that _______
A. people have been allowed to travel freely within the country
B. people have not been permitted to travel freely for various reasons
C. travellers have to carry special papers such as　passports and visas
D. customs posts are necessary at the borders of　the countries
7. Some governments limit the freedom of communication because___
A.  they intend to keep their national secrets unknown to others
B.  they think such freedom will lead to wars
C.  they often disagree with each other on important matters
D.  they want to show their authority over communication
8. We may learn from the passage that _______
A. people do not care about the removal of barriers between countries
B. people can not remove the obstacles made by themselves
C. man-made barriers are sometimes harder to overcome than natural ones
D. barriers should be taken for granted as they always exist
9. Which of the following can serve as the best title of the passage?
A. Barriers Made by People               B. Functions of Communication
C. Restrictions on Transportation           D. Progress of Human Society
10．Which is NOT mentioned as the possible limits some countries put on foreign visitors?
A. They have to get a visa before they enter the country.
B. Only a limited number of visitors are allowed to enter the country every year.
C. Not every part of the country is open to foreign tourists.
D. They have to report to government officials when they come to a new place.