Water is a shape shifter: familiar in its liquid and frozen forms, it is invisible in its third form, as a vapor, until it coalesces into clouds overhead or shrouds us in ghostly fog.

• 水有多种形态，我们更熟悉的是液态水和固态冰，它的第三种形态是看不见的水蒸汽，后者升上天空后会聚集在一起形成云团。