Which type of marine boiler has water and steam inside the tubes with hot combustion gases passing over the outside of the tubes?

Why C is correct

In a water-tube boiler, the water and steam are inside the tubes and the hot combustion gases pass over the outside. This is the opposite arrangement from the fire-tube (Scotch) boiler, in which hot gas runs through tubes surrounded by a large drum of water. Marine boilers are almost always water-tube type.