Which reappeared word indicates the author’s uncertainly about where the twins’ characteristics came from?

Humans have survived and thrived in mexico city by using technology to create greater access to land. when the spanish conquered the aztec capital, tenochtitlan, in the 16th century, they built mexico city by draining the lakes and filling in the lake water to create more arable land for agriculture. this technique of land reclamation has continued to be fundamental to human civilization in mexico city. 

Conflicts arising from drug cartels and goverment corruption is an issue that would most likely be considered as mexico's most challenging problem of today. the correct option among all the options that are given in the question is the third option or option "c". this problem has continued for a very long time.