Antifreeze is a liquid  that is added to water to keep it from freezing. When water freezes and turns to ice,it expands .The force of water expanding is so great that it will break the hardest metal.Water is used in car engines  to keep them cool while they run,and if this water is allowed to freeze in winter it can break the iron block of the engine.That is why antifreeze is necessary. Water freezes at 0degC;the usual kind of antifreeze will not freeze until the temperature is-40degC.A mixture  of five parts of water and four parts of antifreeze will prevent freezing at-18degC;four parts of water and five parts of antifreeze reduce this to -22degC. Alcohol is a kind of good antifreeze,but when the air is running it becomes hot and the alcohol boils away,so it must be changed very often.Most people use antifreeze that does not boil away when the engine is running.There are several chemicals that do this.One of the most popular is called ethylene glycol. The usual kind of antifreeze freezes at   _  .
0degC -18degC -22degC -40degC