填空题
[听力原文]
Whenever you visit a foreign country, you must carry a passport. This document contains your photograph and gives your name, country, place and date of birth, height and any distinguishing marks. These details are checked by customs officers at the airport. They are trained to make sure that the photograph and details in your passport match your appearance.
Customs officers also check the passports of people returning from a foreign country. This is called immigration control. Some passengers may have to carry a special entry form called a visa. This allows them to stay in a country only for a given length of time.
If a customs officer suspects a passenger, he or she can feed the passport number into a computer. This will check the number to see if the passport is stolen or belongs to someone wanted by the police.