The ability of mammals to control their internal body temperatures is a factor in the development of their brains and intelligence. This can be seen from the following facts: the brain is a chemical machine, all chemical reactions are temperature dependent, and any organism that can control its body temperature can assure that these reactions occur at the proper temperatures. Which one of the following is an assumption on which the argument depends? ['Organisms incapable of controlling their internal body temperatures are subject to unpredictable chemical processes.', 'Organisms unable to control their body temperatures do not have the capacity to generate internal body heat without relying on external factors.', 'The development of intelligence in mammals is not independent of the chemical reactions in their brains taking place at the proper temperatures.', 'The brain cannot support intelligence if the chemical reactions within it are subject to uncontrolled temperatures.']