To become a citizen of the united states, you must

Follow all immigration procedures provided by the US. (VISAs, etc)

You must get a U.S. citizenship. If you meet certain requirements, you may become a U.S. citizen either at birth or after birth.
 To become a citizen at birth, you must: 
Have been born in the United States or certain territories or outlying possessions of the United States, and subject to the jurisdiction of the United States.

To become a citizen after birth, you must:

Apply for “derived” or “acquired” citizenship through parents and or apply for naturalization.

Your answer should be choice b!