听力原文： Ensuring the safety of passengers and aircraft is a major concern at airports. Security personnel operate metal detectors and X-ray machines that screen baggage for possible weapons or illegal substances. Security personnel also require that each passenger show photo identification before entering an aircraft. Many areas of an airport, especially those areas that contain critical equipment, are protected by security personnel and are off-limits to the public. In the wake of the September 11, 2001, terrorist attacks in the United States, airport security became the responsibility of the federal government. The United States Congress enacted the Aviation and Transportation Security Act in response to the attacks, which bad exposed a number of weaknesses in airport and airline security. The new law expanded the number of baggage screeners, imposed standards for their training, and made them federal employees for a period of time. Beginning in January 2002, it required that all passenger luggage, including checked luggage, be screened. By the end of 2002, all checked luggage was to he put through special explosives-detecting devices. The law increased the number of armed federal air officials flying on domestic flights and required international airlines to turn over advance copies of their passenger lists to U.S. Customs officials for background checks to screen out suspected terrorists. (26)