The correct answer is C) The pressure will prevent the components from being tightened. When there is pressure in a hydraulic system, attempting to tighten a leaking fitting will be extremely difficult, if not impossible. The high pressure inside the system will act against your efforts to tighten the fitting, preventing you from being able to successfully stop the leak. Trying to tighten the fitting under pressure could also potentially damage the components or lead to further leaks. The other answer choices are incorrect because A) vibration is not a likely outcome, B) you will not be successful in tightening the fitting under pressure, and D) dislodging scale is not the primary issue when tightening a fitting with the system under pressure.