Clouds Clouds are classified according to how they are formed. There are two basic types: (1) Clouds formed by rising air currents. They are piled up and puffy. They are called “cumulus” which means piled up and accumulated. (2) Clouds formed when a layer of air is cooled below the saturation point without vertical movement. These are in sheets or foglike layers. They are called “stratus”, meaning sheetlike or layered. 请分析以上段落所用到的写作手法以及段落的组成部分。