单项选择题 The resistance to the movement of the globule in oily water mixture depends on its size and the （） of the fluid.

单项选择题 The principle of separation by which all commercially available oily water separators function is （） differential between oil and water.

单项选择题 In a domestic fresh water system, the pump starters are controlled by （） switches which operate when the pressure in the tank varies within predetermined limits as water is drawn off.