Answer:
C. the temperature and amount of rainfall in a biome
Explanation:
Not enough oxygen
rainforests will turn into desserts like the Sahara dessert which use to be a tropical place.
Overcrowding and slums developed in many impoverished countries in the 20th century, mostly due to large migrations to cities from people looking for work.
Natural resources made people be able to live their life and it all had to do with their geography