Question

1. which is the most common way to become a citizen of a country?

be born in their country of citizenship
have one parent who was a citizen of the country
go to college in a country
marry someone who was already a citizen

Explanation:

Citizenship by birth (jus soli - being born on a country's territory) or citizenship by descent (jus sanguinis - having a citizen parent) are common ways. Among the options, being born in the country or having a citizen parent are typical. Being born in the country is a very common form of acquiring citizenship.

Answer:

be born in their country of citizenship