In 2009,Chinese citizens ____ the largest group of immigrants to Australia,

题目

In 2009,Chinese citizens ____ the largest group of immigrants to Australia,
taking place of the traditional sources of Britain and New Zealand.
A becomes B was becoming C became D has become
请说出答案,并给予解析,谢谢!

答案

C
在2009年,中国成为澳洲的最大移民团体.
由于是简单陈述过去事实,用C的过去时态更加准确.