Concept:Large-scale urban migration is mainly driven by the pull of industrial jobs in cities.
Explanation:Industrial development created many factory jobs in urban centres.
These jobs attracted large numbers of rural dwellers seeking better incomes and living standards.
Improved medical services and transportation supported city life but did not start the mass movement.
High demand for manufactured goods was a result of industrial growth, not the main cause of migration.
Thus, the beginning of large-scale rural-to-urban migration is linked to industrial development.
Answer:A. industrial development.