A firetube boiler is one which has
a) water on the inside of the tubes and the hot gas of combustion on the outside.
b) the furnace as the first pass of the burner flame.
c) water on the outside of the tubes and hot water on the inside of the tubes.
d) water on the outside of the tubes and the hot gas on the inside of the tubes.
e) internally fired tubes surrounded by water.
Answer: D