Subject + 变成 + 了 + New State
The verb 变成 (biànchéng) means "to become" or "to turn into." It indicates a change of state, form, or identity from one thing to another. For example, 毛毛虫变成了蝴蝶 means "The caterpillar turned into a butterfly."
几年不见,这个小镇变成了一座现代化城市。
Jǐ nián bújiàn, zhège xiǎo zhèn biànchéng le yí zuò xiàndàihuà chéngshì.
After not visiting for a few years, this small town has turned into a modern city.
天气突然变冷,雨变成了雪。
Tiānqì tūrán biàn lěng, yǔ biànchéng le xuě.
The weather suddenly turned cold, and the rain turned into snow.
他通过努力学习,变成了一名优秀的工程师。
Tā tōngguò nǔlì xuéxí, biànchéng le yì míng yōuxiù de gōngchéngshī.
Through hard work and study, he became an excellent engineer.