Most clouds and almost all precipitation are produced by the cooling of air as it rises. When air temperature is reduced, excess water vapor in the air condenses into liquid droplets or ice crystals to form clouds or fog.
- precipitation [priˌsipiˈteiʃən] n. 降水
- reduce [riˈdju:s] v. 减少
- excess [ˈekses] adj. 过量的
- vapor [ˈveipə] n.蒸气
- condense [kənˈdens] v. 浓缩，凝结
- droplet [ˈdrɔplit] n.小滴
- crystal [ˈkristəl] n. 晶体
- fog [fɔɡ] n.雾
