When preparing to hydrostatically test water-tube boilers, you should __________.

Correct Answer: Option D — fill the boiler with water not less than 70°F (21.1°C), nor more than 160°F (71.1°C)

Title 46 CFR mandates that hydrostatic test water temperature must be maintained between 70°F and 160°F to prevent brittle fracture of the boiler steel while ensuring accurate structural integrity assessment.