中国五年前根本没有高速铁路。但是现在高铁列车(high-speed trains)的票经常很快就售罄，尽管发车间隔比较短。人们能够很方便地以两倍于美国火车最髙速的速度在全国周游。高速铁路系统的运菅非常成功，它运载的乘客是全国民航 (civil aviation)系统运载的乘客的两倍。中国有世界上最先进的、低排放的快速运输系统之一，而做到这一点仅仅用了五年。

参考译文：

China didn't have a high-speed rail five years ago.Butnow the tickets of high-speed trains are usually soldout very quickly, even though the departureinterval is quite short.And people can convenientlytravel around the nation at a speed that doubles thespeed of the fastest American train.The operation of high-speed rail system is very successful;it carries twice as many passengers as the nation's civil aviation system.China has one of themost advanced rapid transit systems with low emissions in the world, and it only takes fiveyears to achieve this.

解析：

1.但是现在高铁列车的票经常很快就售罄，尽管发车间隔比较短:“售罄”可译 为sell out，意为“卖完了，卖光了”;“发车间隔”译为departure interval。

2.人们能够很方便地以两倍于美国火车最高速的速度在全国周游:“以...的速度”可译为at a speed...，speed意为“速度”;“两倍于”即“是...的两倍”，可译为double,也可译为twice。四级报名时间

3.高速铁路系统的运营非常成功，它运栽的乘客是全国民航系统运载的乘客的两倍:“运栽”可用carry来表示。“倍数+as+many/much/large等形容词+(比较的内容)+as”为英语中表达倍数时常用的结构，中间的形容词根据比较的内容来定，如比较大小则用as large as,表示“是...的两倍大”则为twice as large as。