The correct option is B Both A and R are correct, and R is the correct explanation of A.
Large-scale industries produce capital and basic goods for other industries. In a way, they drive the whole process of industrialisation. They produce goods like railway engines, railway wagons, trucks, motors, planes, electrical equipment, transformers, telephones, radios, transistors, and so on. All these are necessary to develop infrastructure of other industries. Thus, they help in economic development.