Right answer is (a) Fire tube boiler
To elaborate: Cornish boiler is an example of fire tube boiler and also includes Cochran, Lancashire, and Locomotive and scotch marine boilers. Fire tube boilers are those in which the products of combustion pass through the tubes and water lies around the outside of tubes. These boilers operate at moderate pressure (16-20bar) and more suitable to generate 3-8 tons of steam per hour which is used in process heating.