下列关于自然现象中霜、云、露、雾等的形成的说法中，正确的是（ ）
A．霜是大量的小水滴遇冷凝固形成的小冰晶
B．云是水蒸气遇冷液化成的水滴及凝华成的冰晶组成的
C．露是大量的小冰晶吸热熔化成的小水滴
D．雾就是空气中大量的水蒸气汇聚形成的
A、空气中的水蒸气骤然遇冷，迅速放出大量的热，直接变成的固体小冰晶，附着在地面上的花草树木、石块上，就是霜，属于凝华现象，不是凝固，故A错；
B、云是由水蒸气遇冷液化成的水滴、凝华成的冰晶组成的，正确；
C、春秋天，空气中的水蒸气遇冷液化成小水珠附着在地面上的花草树木上，就是露，故C错；
D、春秋天，空气中的水蒸气遇冷液化成小水珠附着在空气中的土壤颗粒上，就是雾，而水蒸气是看不到的，故D错．
故选B．
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