What is meant by the critical temperature?

• The critical temperature is the ambient temperature at which the cow can no longer maintain its body temperature herself
• The cow's upper critical temperature is reached at --Select-- 25°C 22°C 20°C The lower critical temperature is reached at --Select-- -25°C -22°C -20°C .
• A cow feels most comfortable at an ambient temperature between --Select-- 4°C to 18°C 10°C to 14°C -4°C to 18°C .