Passage One Questions 21 to 25 are based on the following passage. Your passport is your official identification as an American citizen. In America，most people never consider obtaining a passport unless they are planning a trip out of the country. In Europe, where travel from one country to another is much more common，almost everyone carries a passport. A passport is final proof of identity in almost every country in the world. In 1979 almost 15 million Americans held passports. Most of these passports were obtained to travel outside the country because，except for a few Western nations。passports are required to enter every country. And if you travel abroad，you must have a valid passport to reenter the country. When traveling abroad，you will need a passport for identification when exchanging dollars for francs or marks or other foreign currency. You may also need your passport to use a credit card，buy an airplane ticket or check into a hotel. As a passport is an official U. S. document. it is valuable as identification in any emergency cases，such as floods，fires，or war. Don't confuse passports and visas. Whereas a passport is issued by a country to its citizens. a visa is official permission to visit a country granted by the government of that country. For some years，many countries were dropping their visa requirements，but that trend has reversed. Argentina，Brazil，and Venezuela now require visas from U. S. citizens. They may be obtained from the embassy of the country you wish to visit. Passport applications are available at passport agency offices in large cities like Boston，New York，or Chicago. In smaller cities，applications are available at post offices and at federal courts. To get your first passport，you must submit the application in person. along with a birth certificate and two pictures. The main purpose of this passage is to______.