The correct option is B Reduction with CO
In extraction of iron from its oxide ore, hot air in blown from bottom of blast furnace so that coke is burnt to give high temperature upto 2200 K at lower portion of furnace only.
Then, CO and heat moves to upper part of furnace.
The temperature is lower in upper part where the iron oxide get reduce in different temperature.
At 500-800 K, iron oxide get reduced only by CO.
At 900-1500 K, iron oxide is reduced by both C and CO.
Limestone is added to the furnance to remove the SiO2 as slag (CaSiO3).