Water Cycle is the answer
Answer: here´s why
Explanation: Underneath the frozen upper layer, the water remains in its liquid form and does not freeze. Also, oxygen is trapped beneath the layer of ice. As a result, fish and other aquatic animals find it possible to live comfortably in the frozen lakes and ponds. If water is heated, its volume gradually decreases.
The most important compound in living beings includes nucleic acid, carbohydrates, proteins and lipids