单选题：根据下面资料，回答题 How Customs Work A．One of the little rituals all

根据下面资料，回答题
How Customs Work
A．One of the little rituals all international travelers go through is customs．To most people, this is justanother stop in an alrport or a minor inconvenience at a country's borders．But when you go throughcustoms, you are actually taking part in a key component of the global economy.
B．A nation's customs service has many responsibilities．At its most basic level, its purpose is toregulate what comes into and goes out of a country．The foremost element of this regulation iscontrolling international trade．The concept of trade is as old as civilization itself．If my tribe has ahuge supply of bananas, and your tribe has a huge supply of fur, we will trade goods so that bothour tribes can eat and both can keep warm．In the modern world, international trade is based onmoney, but it works in pretty much the same way．My country may produce more televisions thanthe population needs, but not enough cars．In order to have everything the population needs,businesses in my country will export TVs and import cars.
C．Any nation wants its own businesses to do well, so most of the time they prefer their people buydomestic goods over competing foreign goods．But in many cases, goods are available cheaper inanother country than in your country, and people naturally want to buy them at the lower price．Totilt the balance in favor of domestic businesses, governments impose tariffs, also called duty, onforeign goods coming into the country.
D．In addition to encouraging domestic trade, duty also gives the nation a "piece of the action" whensomebody buys something produced overseas．Customs agencies are often major sources of revenuefor the government．The U．S．Customs Service, for example, brings in more money than any othergovernment office except the Internal Revenue Service．To control specific sorts of trade, agovernment may impose a higher tariff on certain types of goods ( alcohol, for example)．Certaincountries may join together to work out mutually beneficial trade agreements, enabling businesses inthose nations to trade more freely with each other than they can with businesses in other nations.
This gives an advantage to nations that a country has a good relationship with.
E) Customs agencies also monitor what is being exported from a country．For example, mostgovernments strictly regulate what weapons can be exported to other nations．This is simply acommon-sense safety measure: It's not a good idea to ann enemy nations, so the government has toknow who is buying any domestically-produced weaponry．As we'll see later on, customs agenciesalso pay careful attention to how much money citizens are transporting out of the country.
F) Duty charges have a huge effect on big businesses, which may import millions of dollars worth ofgoods every year．To regulate trade on this level, a country's customs agency must keep track of allshipments that come into the nation's ports or cross its borders．They can't check every bit offoreign cargo, of course, so agents pick certain boxes to inspect and certain shipments toscrutinize．In an effort to speed up the process, the U．S．Customs Service is implementing new,computerized systems for processing shipments and charging importers.
G) While large businesses are the main importers in a country, trade restrictions also apply to theindividual traveler．When you bring home souvenirs (纪念品) from another country, you areactually importing goods．In the United States and many other countries, the customs agency grantseach traveler a nominal duty exemption ( 免除 ) to allow them to bring back a reasonable amount ofgoods without having to pay tariffs.
H) In most countries, it isn't feasible for the customs agency to check all of the goods that every singletraveler is importing, so governments have to depend largely on people's honesty．When you enter acountry, you are asked to truttffully report what goods you are importing and make a good faithestimate of their value．They don't put their entire trust in people's good character, of course;customs performs a thorough search of some percentage of all travelers.
I)Some customs agencies decide which travelers to search based on random chance．You are asked topress a button on a machine that activates a random number generator．Depending on the numberthat comes up, either a green light comes on and you can pass through or a red light comes on andthe agent searches your bags．Other customs agencies decide who to search based solely onintuition．After many years on the job, a customs agent develops a keen eye for people who are upto no good．Unlike the police, customs agents are fully authorized to search your luggage, clothesand even your body without any warrant or reason for suspicion．Customs agents often work side-by-side with immigration officials, and in some ports of entry, one inspector may represent bothagencies．But at its core, a customs agency is concerned with the things that are coming in and outof a country, rather than the travelers themselves.
J) In addition to monitoring legal imports, a nation's customs agency also works to keep out illegal orcontraband (违禁品 ) items.Customs agencies must fight the flow of illegal materials acrossborders．In addition to drugs, customs agencies may watch for weaponry, child pornography ( 色情资料), counterfeit merchandise and stolen goods．They also watch for people carrying illegallygained money across borders.
K) These sorts of illegal materials make up only one category of contraband goods．Customs agents alsostop the importation of legal goods that are a threat to the nation's security．In most countries, theimportation of fruits, meats, animals and plants is heavily regulated due to the fear of disease orecological imbalance．While it may seem strange that a piece of fruit is considered a threat tonational security, the risk of biological contamination is very real．In the late 1980s, one travelerwith one piece of contaminated fruit caused an infestation (大量滋生) of Mediterranean fruit fliesthat destroyed millions of dollars worth of crops in California.
L) Some completely harmless items are deemed contraband simply because of the country they comefrom．If country A is considered to be a national enemy of country B, or has a record of violatinginternational law, country B ( and other countries) might institute an embargo ( 禁运) against thatcountry ( a ban on the importation of country A's goods)．This cuts off potential business for country
A, and this may persuade its leaders to change their policies．In the United States, the best knownexample of this sort of sanction is the embargo against Cuban products．There is a high demand forCuban cigars in the United States, but they are strictly regulated because of the strained relationshipbetween the United States and Cuba．As with drugs, smugglers are eager to sneak in a supply tomeet this demand, and are constantly trying to get around customs.
M) In many countries, the customs agency closely monitors the importing and exporting of cultural artifacts．While a traveler may have purchased the item in good faith, it might have been stolen at an earlier point．Customs agencies have helped to restore many priceless artifacts to their rightful owners.
N) A country's government might also ban importation of items based on ethics and morality．Forexample, in many countries, you cannot import ivory or other products that come from endangeredanimals．In 2000, the United States enacted the Dog and Cat Protection Act, banning the importationof any products made from dog and cat fur that was acquired inhttmanly．The U.S．Customs Serviceconfiscates all such goods so that U.S．citizens do not inadvertently support this practice.
O) Without customs agencies, nations would have no control over what comes in and goes out of theircountry．In order to protect its citizens and businesses, a government has to be vigilant in protectingits borders, not only against armed attack, but also against unwanted imports．As any customsagent will tell you, this is crucial to maintaining order in modern society.
Some countries are able to do businesses more freely with each other, if they make tradeagreements in favor of both sides.