The correct answer is D) in a position screened from the furnace. In a boiler equipped with a convection-type superheater, the superheater tubes are located in a position screened from the furnace's radiant heat. This is done to prevent excessive heating of the superheater tubes, which could lead to premature failure. The superheater tubes are positioned downstream of the generating tubes, where they are exposed to the convective heat of the flue gases, but shielded from the direct radiant heat of the furnace. The other options are incorrect because: A) the superheater tubes are not located between the economizer and generating tubes, B) they are not positioned between the downtake nipple and circulator tube, and C) they are specifically designed to be shielded from the direct radiant heat of combustion.