When vapor cools, it makes clouds.

当水蒸气冷却时，就形成云。

同一单元的其他句子

• Rain comes from clouds.雨来自云。
• The water cycle is important.水循环很重要。
• Where does rain come from?雨从哪里来？
• Clouds are made of water drops.云是由水滴组成的。
• Rain falls from the sky.雨从天空落下。