big as the population of the United States.

扩大后的欧盟人口超过五亿，是美国人口的两倍之多。

　　【剖析】 1)twice as big as the population of the United States相当于一个非限制性定语从句，修饰前句的population。

2)expanded是expand的过去分词形式，作前置定语，修饰European Union，表示被动，相当于"The European Union which has been expanded"。

　　【拓展】1）twice as big as是英语中表示倍数的句式之一。通常有以下几种:

　　A is 4 times as big/long/high as B.

　　A is 3 times bigger/longer/higher than B.

　　A is 4 times the size/length/height of B.

　　2）population表示"人口"。表示"人口多"时，用a large population；表示"人口是多少？"用"How big is the population?"相当于"How many people are there?"