注：文本及音频选自《新托福iBT词汇分类突破》Unit129-130；单词释义主要来自《美国传统词典》。　　Clouds, and almost all precipitation, are produced by the cooling of air as it rises. When the air temperature is reduced, excess water vapourin the air condensesinto liquid droplets, or ice crystals. A fogis formed when thi...