Explanation

(a)
In the blast furnace, iron ore is reduced by coke and carbon monoxide at different temperatures.
$C + O_{2}\ \longrightarrow {CO}_{2}$
${CO}_{2} + C\overset{1500℃}{\rightarrow}2CO$
$3{Fe}_{2}O_{3} + CO\overset{400℃}{\rightarrow}\ 2{Fe}_{3}O_{4} + {CO}_{2}$
${Fe}_{3}O_{4} + CO\ \overset{600℃}{\rightarrow}3FeO + {CO}_{2}$
$FeO + CO\ \overset{700℃}{\rightarrow}Fe + {CO}_{2}$