What allowed native americans in mexico to settle cities larger thsn those in areas to the north
a. the use of advanced engineering methods learned in asia
b. the development of cities that were built by an earlier civilization
c. the use of farming to feed a larger population
d. the requirement of their religion to have large cities

I believe the answer is: b. the development of cities that were built by an earlier civilization

The earlier civilisation in mexico is most commonly known as the Aztecs. In the past, Aztecs were known as one of the most advanced civilisation and known for their development in agricultural technologies (most notably their irrigation system). Native american that came to this area could directly used things that are left over from the past civilization.

yellow fever and other tropical diseases

the answer is b: the religion they practice.

here's why:

there were many different native american tribes and those with similar characteristics formed a main tribe or nation. each had its own language, religion and customs.