单项选择题 Care must be taken to condition the （）in the boiler to prevent scaling, and corrosion, which can weaken the pressure vessel.

单项选择题 The power and torque capability of the steering system must be such that the rudder can be swung from （）one side to（）the other side with the ship at maximum speed.

单项选择题 Certain requirements must currently be met by a ship’s steering system.There must be （）independent means of steering, although where two identical power units are provided, an auxiliary unit is not required.