What is one responsibility that is only for United States citizens?

Why this is the answer

Serving on a jury and voting in a federal election are the two duties reserved for citizens, and naming either one earns full credit. The jury answer makes the most sense once you see how often the Constitution relies on juries. Article III requires that the trial of all crimes, apart from impeachment, be by jury. The Bill of Rights goes further: the Sixth Amendment promises anyone accused of a crime a speedy and public trial by an impartial jury, and the Seventh preserves jury trials in civil suits where more than twenty dollars is at stake. Those promises only work if ordinary people show up to decide cases, and the USCIS lessons for this version point out that juries are made up of U.S. citizens, whose participation helps keep trials fair. Voting is the other half, and it differs from jury service in one respect. No law forces a citizen to vote, so it is a responsibility in the civic sense rather than a legal requirement. The lessons describe it as central to any democracy: through the ballot, citizens choose leaders to represent their ideas, and those leaders are expected to look after their interests. What trips people up is the word only. Paying taxes and obeying the laws are real responsibilities, but the same lessons note that everyone living in the United States shares them, citizen or not, so neither can be the answer here. Be careful, too, with “vote” on its own. The official wording says a federal election, and that qualifier matters because permanent residents may take part in some local or state elections that do not require citizenship. A quick self-check before you answer: ask what a green card holder cannot do for the country. Sitting on a jury is one, and casting a ballot in a federal election is the other. Either of those, said in the words of the official list, is a complete answer.