cloud with vertical development

例句：

1. 1. The cloudswere so thick that they obscured thesun.
   云层很厚，遮住了太阳。
2. 2. The weatherforecast predicted a cloudy day.
   天气预报预测会是一个多云的日子。
3. 3.The clouds moved slowly across the sky.
   云朵缓缓地在天空中移动。