The correct answer is A) remove all inspection plates and manhole covers as required by the marine inspector. When preparing to hydrostatically test water-tube boilers, you should remove all inspection plates and manhole covers as required by the marine inspector. This allows the inspector to thoroughly inspect the interior of the boiler and ensure its integrity before the hydrostatic test is conducted. The other answer choices are incorrect because: B) is not necessary for the hydrostatic test itself, but may be required during other inspections. C) is not relevant, as the boiler should be at ambient temperature for the hydrostatic test.