(A) Iron and Steel
With the expansion of railways in England from the 1840s and in the colonies from the 1860s, the demand for iron and steel increased rapidly.
The passage from Chapter 4, Section 1.2 directly states that after the 1840s, the iron and steel industry led the way, and railway expansion drove up its demand. Cotton was dominant before the 1840s, making (B) incorrect. Aluminium/Bauxite and Copper are not mentioned in this context.