Concept:Certain micro-organisms survive only in extreme environments where they have unique adaptations.Explanation:Most organisms cannot survive in high salt concentrations because water leaves their cells. Halophiles are specially adapted micro-organisms that thrive in salty water. They maintain their internal water balance by producing compatible solutes or by balancing salt concentrations inside and outside their cells. Humid air, moist soil, and mouth cavities do not require such extreme salt-specific adaptations. Therefore, salty water is the habitat where only specially adapted micro-organisms are found.Answer:A. Salty water