tiān qì / yí rè / tā / jiù / bǎ / hòu / niú zǎi kù / huàn chéng le / qīng biàn de / dān kù

天气一热，他就把厚牛仔裤换成了轻便的单裤。

As soon as the weather gets hot, he changes from heavy jeans into lightweight unlined trousers.