Iron and Steel Industry II

Q. <!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> In iron production, coking coal and limestone are also used apart from iron ore. What is the proportion required for the production?

1. 1 : 1 : 1
2. 2 : 1 : 1
3. 3 : 2 : 1
4. 4 : 2 : 1