As Societies Moved from Rural Living to Living in Cities,human

As societies moved from rural living to living in cities,human fertility decreased.Why?

A) The polluted environments of cities made it harder to raise children to maturity.
B) Children were more expensive to raise in cities, and child labor was less beneficial.
C) In cities, there was too little food to ensure that children would survive to adulthood.
D) Children working in the newly invented factories of the Industrial Revolution tended to have shorter lifespans.