冬天，温度可能降到零下15度。

In the winter, the temperature can drop to 15 degrees below ___zero.

我们必须认识到，狮子生活在冬天温度可能降到零度以下的国家是不自然的。

We have to learn that it is not natural for a lion to live in a country where, in winter, the temperature can fall below ___zero.

水在零摄氏度时结冰。

Water freezes at ___zero degrees Celsius.