表面结硬皮；结成硬壳
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表面结硬皮；结成硬壳；表面结硬皮；结成硬壳
to become covered with a hard, dry outer layer
By morning, the fresh snow had crusted over.
到早晨时,新雪表面已经结了一层硬壳。
表面结硬皮；结成硬壳
to become covered with a hard, dry outer layer
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