It is believed that a mother language developed somewhere in
africa
eurasia
europe
asia

The correct answer is - Africa.

The mother language of all languages that exist in the present is considered to be a language that developed on the African continent. The reasons for this theory is that some African languages have remained mostly unchanged until the present, and by studying them, they linguists have managed to find the basic traits for the development of the other languages around the world. Also,  a big reason for this theory is that the Homo sapiens appeared in Africa, and after that moved on the other continents. Since it is sure that the Homo sapiens used some form of primitive language, it's easy to assume that it was the mother language of all the other languages that appeared latter in the history.

the aztec capital was built on a lake.

explanation:

tenochtitlan was built on lake texcoco.

hope this : )