专业四级是针对英语专业同学的重要考试，其真题的参考价值无可比拟，希望同学们能够吃透真题，通过专四。
Hints:
U.S.
The Airline Monitor
Delta/Northwest
Richard Aboulafia
Few people expect luxury while flying, but these days, even the basics seem to be in bad shape. It's not uncommon to find your tray table broken, the in-flight entertainment system not working and your seat cushion worn. All of this can make you think: how old is this plane anyway? The reality for many U.S. air travellers is that most of their journeys take place on planes that have been in service for a decade or more. The average age of the fleet of the seven large U.S. passenger airlines is about 14 years old, according to The Airline Monitor. It found American and Delta/Northwest had the oldest fleets, at about 16 years on average. As of the end of 2008, a small percentage of the merged Delta/Northwest's planes dated back to the late 1960s. U.S. fleets are among the oldest in the world, said Richard Aboulafia, an aviation analyst. "I'm not really sure that people should read that much into that," Aboulafia said. "From a safety standpoint, a lot of the older planes were built tougher and with proper maintenance. There's no reason why a plane can't stay safe for 25 to 30 years." It's also important to remember that a plane may be 20 years old, but its engines and other major systems could have been recently manufactured or upgraded, said Aboulafia. There's less pressure on the airlines to upgrade the interior, unless it's a safety issue or a redesign that will save money.