become多指身份、职位等的变化,它强调变化的过程已经完成,后面可接名词或形容词.例：
He becomes a teacher.他成了一名老师.
Her mother became angry when she heard the news.
她妈妈听到这个消息时非常生气.
get多用于口语,表示一种变化过程,强调的是“渐渐变得”,后常接形容词的比较级形式.
It’s getting darker and darker outside.户外天色越来越暗.
In winter the days get shorter.冬季白天变得较短.
turn指在颜色和性质等方面与以前的完全不同,强调变化的结果.
Leaves turned brown in the mountains.山里的树叶已变成了棕色.
The milk has turned bad.牛奶变质了.