| In most marine boilers, the primary reason the first few rows of generating tubes, called screen or furnace row tubes, are made larger in diameter than the rest of the generating tubes is because __________. |
| A) they require more water flow since they are exposed to the greatest heat |
| B) they must screen the superheater from the direct radiant heat of the burners |
| C) they must act as downcomers to ensure proper circulation |
| D) their main function is to retard combustion gas flow for maximum heat transfer rates |
