Since 1 month 15 this year, there has been a rare snowfall and freezing weather in our city for decades. Bad weather has caused some disasters, such as water, electricity and electricity.

(1) When liquid water turns into ice, the gap between water molecules increases and the volume of ice becomes larger, which leads to the rupture of water pipes and water meters.

(2) Because the freezing point of salt solution is lower than the freezing point of water, road workers can accelerate the melting of ice and snow by sprinkling salt on the snowy roads.

(3) Topdressing urea [chemical formula: CO (NH _ 2) _ 2] outside the roots for 2-3 times in the germination stage can promote the growth of citrus trees. "Urea Co (NH _ 2) _ 2 contains nitrogen and belongs to nitrogen fertilizer. The mass ratio of carbon to hydrogen in urea is = (12× 1): (.

So the answer is: (1) increase (2) snow melting (3) nitrogen, 3: 1.