Which development was the CAUSE of the other three in western europe?
a. growth of the factory system
b. air and water pollution
c. decrease in percentage of people working as farmers
d. increase in the number and size of cities
This one is the cause: growth of the factory system.
Growth of the factory system lead to pollution (from the factory chimneys), it made people move from farms to the cities and as a result the number and size of cities increased.