The answer is "c. jus soli".
Jus soli refers to a Latin expression that implies law of the soil. In certain nations, jus soli system is followed. As indicated by this principle, citizenship of an individual is dictated by where an individual was born. Jus soli is the most widely recognized intends to procure citizenship of a country.
In the U.S., jus soli system is followed to decide citizenship. This implies whoever is born in the U.S. also, is liable to its jurisdiction is naturally granted U.S. citizenship.