In the context of population migration during the Industrial Revolution, one of the effects was the growth of cities (Option B).
1. **Explanation**: As people moved from rural areas to urban centers in search of employment opportunities in factories and industries, cities experienced a significant increase in population.
2. **Example**: Cities like Manchester in England and Pittsburgh in the United States saw a rapid influx of people looking for work in the growing industries during the Industrial Revolution.
Therefore, the correct answer in this case would be Option B: growth of cities.
