Why does an optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation give too low a value for the temperature of a red-hot iron piece in the open, but gives a correct value for the temperature when the same piece is in the furnace?

Options

1. AThe pyrometer is not sensitive to red-hot temperatures.
2. BThe black body radiation in the open interferes with the pyrometer's accuracy.
3. CAn increase in the temperature of open space reduces the radiation energy. When the same piece of iron is plac
4. DThe furnace provides a controlled environment for accurate temperature measurement.