ANS:C - both (a) and (b)

Open-hearth process: A process of steelmaking in which the charge is laid in a furnace (open-hearth furnace) on a shallow hearth and heated directly by burning gas as well as radiatively by the furnace walls.

Duplex process : A process for making steel in which the material is partially treated in a furnace of one type, originally a Bessemer, and then transferred without interruption to a furnace of another type, originally an open-hearth furnace.