urea frost

例句：

1. 1.The farmer sprayed the crops with urea to protect them from the cold.
   农民用尿素喷洒作物以保护它们免受寒冷。
2. 2.The urea frost was so thick that it blocked the sun's rays.
   尿素霜非常厚，以至于阻挡了太阳的光线。
3. 3. The farmers used urea as a fertilizer to improve the soil quality.
   农民们使用尿素作为肥料来改善土壤质量。